Ceramic heater and manufacturing method of ceramic heater

ABSTRACT

The present invention aims to provide a ceramic heater manufacturing method capable of preventing reflection of laser beam at the time of performing trimming by irradiation using a laser beam and performing trimming of a resistance heating element or a conductor layer as designed and the ceramic heater manufacturing method of the present invention comprising the steps of: forming a resistance heating element having a pattern on a surface of a ceramic substrate; and irradiating laser beam onto the resistance heating element to form a gutter or a cut after preceding step so as to adjust a resistance value of the resistance heating element, wherein when the resistance heating element is formed on the surface of the ceramic substrate, the resistance heating element is adjusted so as to have a surface roughness Ra of 0.01 μm or more in accordance with JIS B 0601.

TECHNICAL FIELD

[0001] The present invention relates to a ceramic heater to be usedmainly for production or examination of semiconductors in semiconductorindustries and a manufacturing method of the ceramic heater.

BACKGROUND ART

[0002] Products for which a semiconductor is applied are very importantproducts necessary for a variety of industries and a semiconductor chip,one of the most typical products among them is, for example, produced byslicing a single crystal silicon into a given thickness to manufacture asilicon wafer, and then forming various circuits thereon.

[0003] To form a variety of such circuits and the like, it is requiredto carry out steps of applying a photosensitive resin to a siliconwafer, exposing and developing the resin, and then subjecting theresulting resin to post curing treatment or to sputtering treatment toform a conductor layer. For these steps, the silicon wafer is requiredto be heated.

[0004] As such a kind of a heater for heating a semiconductor wafer suchas a silicon wafer used in the condition of setting the semiconductorwafer thereon, conventionally those equipped with resistance heatingelements such as electric resistors on the bottom face side of asubstrate comprising aluminum are employed most, however the substratecomprising aluminum has a thickness of about 15 mm and therefore isheavy and bulky and not necessarily easy to be handled and insufficientin temperature controllability in terms of the temperature-followingproperty to the electric current application to make even heating of asemiconductor wafer difficult.

[0005] In the publication of JP Kokai Hei 11-40330, there is disclosed aceramic heater composed of a substrate of nitride ceramics or carbideceramics with a high thermal conductivity and strength and heatingelements formed by sintering a metal particle on the surface of aplate-like body (a ceramic substrate) comprising these ceramics.

[0006] Further, as for a heater to be employed for such a semiconductorproducing device, the surface of the resistance heating elements thereofis easy to be affected by light and heat, treatment gases and the likewhen it is used as the semiconductor producing device, thus theresistance heating elements are required to have durability to oxidationon the surface.

[0007] Therefore, the inventors of the present invention have madeinvestigations aiming to form a resistance heating element excellent indurability and consequently found that formation of an insulatingcovering on the resistance heating element formed on a ceramic substratemakes a ceramic heater excellent in durability, for example,anti-oxidation property and the like. However, the insulating coveringmay work also as a heat insulator for the resistance heating element, sothat at the time of cooling after the ceramic heater is heated, quickcooling sometimes becomes impossible.

[0008] Further, as a method for forming the resistance heating elementat the time of manufacture of such a ceramic heater, conventionally, thefollowing methods have been employed; a method for forming theresistance heating element by a coating process such as screen printing;a method for forming the resistance heating element by a physicaldeposition method such as sputtering and a plating method afterproducing a ceramic substrate with a given shape.

[0009] In the case of a method for forming the resistance heatingelement using a coating method after producing a ceramic substrate witha given shape, a conductor containing paste layer in a heating elementpattern is formed and successively heating and firing is performed toform the resistance heating element.

[0010] However, although the resistance heating element can be formed ata relatively low cost, such methods have a problem that the resistanceheating element with a precise pattern can not be formed easily sincetrifling mistakes at the time of printing result in short-circuit in thecase of producing a precise pattern. The above-mentioned method hasanother problem that the printing thickness is not even andsubsequently, the resistivity becomes uneven.

[0011] Further, in the case of a method for forming the resistanceheating element using a physical deposition method such as a sputteringand a plating method, after producing a ceramic substrate with a givenshape, a metal layer is formed in a given area of the ceramic substrateby these methods and successively etching resist is formed so as tocover the portions on heating element patterns and then etchingtreatment is performed to form the resistance heating element in thegiven patterns, or at first the portions other than the heating elementpatterns are covered with resin and the like and then theabove-mentioned treatment is carried out to form the resistance heatingelement in the given patterns on the surface of the ceramic substrate byone time treatment.

[0012] However, although this sputtering or the plating method and thelike is capable of forming precise patterns, the method has a problemthat etching resist or plating resist has to be formed on the ceramicsubstrate surface by a photolithographic technique in order to form theresistance heating element with given patterns, resulting in high cost.

[0013] As a method for solving these problems, a method has beenemployed which has an advantage that precise resistance heating elementpatterns can be formed at a relatively low cost, that is: a methodcomprising steps of forming a conductor layer in a strip-shaped or aring-shaped with a given width and then removing the portions other thanthe heating element patterns using a laser beam irradiating equipmentand the like to form precise heating element patterns; or a methodincluding the steps of forming the resistance heating element by theabove-mentioned method and successively irradiating laser beam to adjustthe thickness of the resistance heating element or to remove someportion of the resistance heating element so as to precisely adjust theresistant value.

[0014] However, by a conventional screen printing and the like, thesurface of the resistance heating element or the conductor layer issmooth and at the time of performing trimming by laser beam irradiation,in some cases, the laser beam is reflected at the surface of theresistance heating element. Consequently, it becomes impossible toperform trimming the resistance heating element or the conductor layeras designed, resulting in unevenness of the depth and the width.

SUMMARY OF THE INVENTION

[0015] Inventors of the present invention have made investigations forsolving the problem that a ceramic heater cannot be cooled quickly andfound that adjustment of the surface roughness of an insulating coveringallows the insulating covering to function just like a heat releasingfin and thus drops the temperature of the resistance heating element atthe time of cooling, as a result, quick temperature drop of the ceramicheater became possible, and completed the first aspect of the presentinvention.

[0016] A ceramic heater of the first aspect of the present invention isa ceramic heater comprising: a ceramic substrate; a resistance heatingelement, which is composed of one circuit or more circuits, disposed ona surface of a ceramic substrate; and an insulating covering provided onthe resistance heating element, wherein said insulating covering has asurface roughness Ra of 0.01 to 10 μm, preferably 0.03 to 5 μm inaccordance with JIS B 0601.

[0017] In the above-mentioned ceramic heater, since the surfaceroughness Ra of the surface of the above-mentioned insulating coveringaccording to JIS B 0601 is adjusted at a range of 0.01 to 10 μm, theinsulating covering functions to keep the temperature of the resistanceheating element to some extent and at the same time if there exists acoolant in the surrounding, the roughened face formed on the insulatingcovering surface works as a heat releasing fin to carry out cooling at arelatively high speed.

[0018] Accordingly, at the time of raising the temperature of theceramic heater, the temperature can be raised quickly and on the otherhand, at the time of cooling after the temperature rise of the ceramicheater, the temperature of the resistance heating element can be droppedquickly and as a result, the ceramic heater can be cooled quickly.

[0019] Further, by adjustment of the surface roughness Ra of theinsulating covering surface at a range of 0.03 to 5 μm, dispersion ofthe temperature rise speed can be made small.

[0020] Further, since the insulating covering is formed on the surfaceof the resistance heating element in stead of forming a metal coveringby plating and the like, at the time of application of electric power ofabout 30 to 300 V to the resistance heating element, the inconveniencethat electric current undesirably flows mainly at the surface of theresistance heating element does not take place, and the insulatingcovering can protect the resistance heating element. Further, even ifthe surface temperature of the resistance heating element is raised byelectric power application, since the resistance heating element iscovered with the insulating covering, oxidation or sulfurization byoxygen and SO_(X) and the like in air scarcely proceeds and change ofthe resistance of the resistance heating element can be prevented.

[0021] The reason why electric current flows easily in a plated portionin the case the resistance heating element is covered by plating is thatthere is a difference between: the resistance of the resistance heatingelement; and the resistance of the plated portion and in such a case,the resistance value of the resistance heating element is required to besmall. However, in the case that the resistance heating element iscovered with the insulating covering, since the covering is aninsulator, no electric current flows in the covered portion and thus,the resistance value of the resistance heating element can be set highand accordingly the calorific value can be designed to be high; or thecross-section of the resistance heating element can be made small toobtain the same heat calorific value.

[0022] If the surface roughness Ra of the above-mentioned insulatingcovering surface is less than 0.01 μm, the heat releasing function ofthe insulating covering deteriorates, so that the cooling speed isretarded at the time of cooling the ceramic heater and on the otherhand, if the surface roughness Ra of the above-mentioned insulatingcovering surface exceeds 10 μm, air easily stagnates in the valley partsof the roughened surface, so that the cooling speed is retarded. Inorder to obtain the insulating covering provided with both of such heatinsulating effect and heat releasing effect, the surface roughness Ra ofthe above-mentioned insulating covering is preferably 0.03 to 5 μm. Thisis because dispersion of the temperature rise speed becomes small. If Rais less than 0.03 μm, heat reflection is high at the interface betweenthe insulating covering and air and on the contrary, if Ra exceeds 5 μm,the effect of the heat release becomes significant to result indispersion of the temperature rise speed. Incidentally, Ra is calculatedby dividing the integrated value of absolute value of the surfaceroughness curve by the measured length, whereas Rmax is the heightdifference between a mountain part and a valley part in the curve of thesurface roughness and both have no mutual correlation.

[0023] In the case the above-mentioned insulating covering is formed ina stretch of area containing a portion on which the circuits are formedso as to cover the resistance heating element comprising, especially twoor more circuits, in a lump, the above-mentioned effects are providedand besides, occurrence of short-circuit and the like in the resistanceheating element owing to the migration of a metal (for example, silverand the like) constituting the resistance heating element can beprevented. Further, also in the case of forming the insulating coveringin the above-mentioned areas, the covering layer can easily be formed byscreen printing and the like in the entire area including the portionswhere the above-mentioned circuits are formed, resulting in the decreaseof covering cost and cost down of the heater.

[0024] The ceramic substrate constituting the ceramic heater of thefirst aspect of the present invention preferably comprises a nitrideceramic or a carbide ceramic. Because the nitride ceramic and thecarbide ceramic are excellent in the thermal conductivity fortransmitting generated heat of the resistance heating element andexcellent in corrosion resistance to a treatment gas in a semiconductorproducing device and therefore suitable for a substrate for a heater.

[0025] In the ceramic heater of the first aspect of the presentinvention, the insulating covering may comprise an oxide type glass.Because the oxide type glass to be employed for these purposes has ahigh adhesion strength to the ceramic substrate and to the resistanceheating element and is chemically stable and excellent in electricinsulation property.

[0026] Further, in the ceramic heater of the first aspect of the presentinvention, the insulating covering can comprise a heat resistant resinmaterial. Because the heat resistant resin material usable for thesepurposes also has a high adhesion strength to the ceramic substrate andto the resistance heating element and is excellent in electricinsulation property and can be formed at a relatively low temperature.Incidentally, heating resistance means usability at 150° C. or more.

[0027] As the heat resistant resin material, one kind or more selectedfrom a polyimide type resin and a silicone type resin can be selected.

[0028] Further in the ceramic heater of the first aspect of the presentinvention, a heating face is a side opposed to the side on which theresistance heating element is formed and a semiconductor wafer ispreferable to be heated on the heating face. It is because the heatgenerated by the resistance heating element is diffused while it istransmitted through the ceramic substrate, so that the temperaturedistribution similar to the resistance heating element patterns ishardly formed and a heat evenness property of the heating face can beassured.

[0029] The semiconductor wafer may be placed on the heating face. Also,through holes or concave portions may be formed in the ceramic substratesurface and then, supporting pins may be installed in the through holesor the concave portions so as to slightly project out of the ceramicsubstrate surface in order to hold the semiconductor wafer in thecondition that it is kept at 5 to 2000 μm from the heating face by thesupporting pins for heating.

[0030] Incidentally, in the publication of JP Kokai Hei 6-13161, thestructure of a ceramic substrate covered with resin is disclosed,however the idea disclosed in the publication is that an object to beheated is put on a resistance heating element and thus, completelydifferent from that of the present invention.

[0031] Further, Japanese Patent gazette No. 2724075 disclosed a methodfor covering the surface of an aluminum nitride sintered body with ametal layer which is formed by: depositing an alkoxide, a metal powder,and a glass powder on the surface of the aluminum nitride sintered body;and firing them. However, this patent relates to a package substrate andhas no description or implication that: the metal layer is a resistanceheating element; the opposite side of the face on which the resistanceheating element is formed is used as the heating face; and theinsulating covering is formed on the resistance heating element.Therefore, the novelty and unobviousness of the present invention cannotbe denied.

[0032] The ceramic heater of the first aspect of the present inventionmay comprise a cooling device. The cooling device includes air-coolingdevice or water-cooling device and the like which are using a coolant.The heat exchange may be carried out: by conducting direct blowing ofthe coolant to the ceramic substrate; or by laying a cooling pipe in theinside of the device or the ceramic substrate.

[0033] As the coolant, gases such as air, nitrogen, argon, helium, andcarbon dioxide can be used and other than these, liquids such as water,ammonia, ethylene glycol and the like are also usable.

[0034] The ceramic heater of the first aspect of the present inventionhas similar effects even in the case of carrying out the cooling.

[0035] Further, inventors of the present invention have enthusiasticallymade investigations for solving the problem that the resistance heatingelement or the conductor layer cannot be trimmed as designed at the timeof performing trimming using laser beam in the ceramic heatermanufacture and consequently found that: in the condition that a surfaceroughness Ra of the resistance heating element or the conductor layer is0.01 μm or more in accordance with JIS B 0601 at the time of theformation of the resistance heating element or the conductor layer onthe surface of the ceramic substrate, the laser beam reflection can beprevented and accordingly the resistance heating element or theconductor layer can be trimmed almost as designed without unevenness,and finally completed the manufacturing method of the present invention.

[0036] That is, a manufacturing method of a ceramic heater of a secondaspect of the present invention is a manufacturing method of a ceramicheater comprising the steps of: forming a resistance heating elementhaving a given pattern on a surface of a ceramic substrate; andirradiating laser beam on to the resistance heating element to form agutter or a cut after the preceding step so as to adjust a resistancevalue of the resistance heating element, wherein when the resistanceheating element is formed on the surface of the ceramic substrate, asurface roughness Ra of the resistance heating element is 0.01 μm ormore in accordance with JIS B 0601.

[0037] Further, a manufacturing method of a ceramic heater of a thirdaspect of the present invention is a manufacturing method of a ceramicheater comprising the steps of: forming a strip-shaped or a ring-shapedconductor layer on a given area of a surface of a ceramic substrate; andirradiating laser beam onto the conductor layer to remove a part of theconductor layer by performing trimming after the preceding step so as toform a resistance heating element having a given pattern, wherein whenthe conductor layer is formed on the surface of the ceramic substrate, asurface roughness Ra of the conductor layer is 0.01 μm or more inaccordance with JIS B 0601.

[0038] In the manufacturing methods of the second and the third aspectof the present inventions, since the surface roughness Ra of theresistance heating element or the conductor layer on the ceramicsubstrate surface according to JIS B 0601 is adjusted to be 0.01 μm ormore, laser beam reflection can be prevented and thus the laser beam canbe absorbed in the resistance heating element or conductor layer and asa result, the resistance heating element or the conductor layer can betrimmed as designed.

[0039] If the surface roughness Ra of the resistance heating element orthe conductor layer on the ceramic substrate surface according to JIS B0601 is less than 0.01 μm, laser beam is reflected, so that the energyis diffused and gutters and cuts smaller than those designed are formed,and it results in too smaller resistance value of the resistance heatingelement than a designed value or formation of the resistance heatingelement in different patterns (width) from designed patterns. In orderto keep the laser beam absorption efficiency high, the surface roughnessof the above-mentioned conductor layer is preferably 0.1 to 10 μm.

[0040] Further, according to the manufacturing method of the ceramicheater of the second aspect of the present invention, since theresistance value is adjusted using laser beam, the resistance value canprecisely be adjusted with little unevenness of the depth and widthwithin a relatively short time and consequently, the temperature of theface for heating a semiconductor wafer and the like (hereinafter,referred to a heating face) can be made even to make it possible toevenly heat an object to be heated such as a semiconductor wafer.

[0041] Further, according to the manufacturing method of the ceramicheater of the third aspect of the present invention, resistance heatingelement patterns with little unevenness of the depth and width can beformed within a relatively short time and the manufacturing cost can belowered and complicated and precise patterns can be formed.

[0042] Accordingly, the ceramic heater having such resistance heatingelement patterns is relatively economical, has complicated and precisepatterns and is capable of keeping the temperature of the heating faceprecisely even.

[0043] A ceramic heater of a fourth aspect of the present invention is aceramic heater comprising a resistance heating element formed on asurface of a ceramic substrate, wherein a gutter or a cut is formed at apart of the resistance heating element, and the resistance heatingelement has a surface roughness Ra of 0.01 μm or more in accordance withJIS B 0601.

[0044] Since the ceramic heater has a high surface roughness of theresistance heating element surface, the atmosphere gas can be stagnated,and thus air in the gutter or cuts of the resistance heating element isprevented from flowing, and consequently, formation of low temperatureportion attributed to the cuts or gutters is suppressed. Accordingly,the temperature evenness of the heating face can further be improved.

[0045] Even in the case laser trimming is performed, when lowtemperature spots are formed owing to the cuts or gutters, thetemperature distribution in the heating face becomes wide even if theresistance value unevenness is made small, however in the ceramic heaterof the fourth aspect of the present invention, such a problem is solvedby making the surface roughness of the resistance heating elementsurface high.

[0046] If the surface roughness Ra of the resistance heating elementsurface is less than 0.01 μm, the atmosphere gas on the surface of theresistance heating element flows, so that the effect to prevent lowtemperature spot formation by the cuts or gutters cannot be achieved.

[0047] The resistance heating element is preferable to be covered by aninsulating layer. In the case a covering layer (glass or resin) isformed on the resistance heating element surface, in the case thesurface roughness of the resistance heating element is higher, thecracking by thermal impact is more difficult to take place.

[0048] Incidentally, in the manufacturing methods of the second andthird aspect of the present inventions and the ceramic heater of thefourth aspect of the present invention, the surface roughness Ra of theresistance heating element surface is preferably 15 μm or less. Becauseif it exceeds 15 μm, unevenness of the width of the gutters or cutsincreases owing to the diffused reflection of a laser beam.

[0049] Further, if the surface roughness Ra of the resistance heatingelement surface exceeds 15 μm, the quantity of heat escaping to theatmosphere gas from the resistance heating element surface increases, sothat the temperature distribution in the heating face becomes large.

[0050] Further, if the surface roughness of the resistance heatingelement exceeds 15 μm, on the contrary, cracks are easy to be formed inthe covering layer owing to thermal impact.

BRIEF DESCRIPTION OF THE DRAWINGS

[0051]FIG. 1 is a bottom plane view schematically showing one embodimentof a ceramic heater according to the first aspect of the presentinvention.

[0052]FIG. 2 is an enlarged figure of a portion of the ceramic heaterillustrated in FIG. 1.

[0053]FIG. 3 is a bottom plane view schematically showing anotherembodiment of a ceramic heater according to the first aspect of thepresent invention.

[0054]FIG. 4 is an enlarged figure of a portion of the ceramic heaterillustrated in FIG. 3.

[0055]FIG. 5 is a bottom plane view schematically showing furtheranother embodiment of a ceramic heater according to the first aspect ofthe present invention.

[0056]FIG. 6 is a graph showing the measurement results of the surfaceroughness of an insulating covering constituting the ceramic heateraccording to Example 1.

[0057]FIG. 7 is a graph showing the measurement results of the surfaceroughness of an insulating covering constituting the ceramic heateraccording to Example 2.

[0058]FIG. 8 is a graph showing the measurement results of the surfaceroughness of an insulating covering constituting the ceramic heateraccording to Example 3.

[0059]FIG. 9 is a graph showing the measurement results of the surfaceroughness of an insulating covering constituting the ceramic heateraccording to Example 4.

[0060]FIG. 10 is a graph showing the measurement results of the surfaceroughness of an insulating covering constituting the ceramic heateraccording to Example 5.

[0061]FIG. 11 is a block diagram schematically showing a laser trimmingequipment to be employed for the manufacturing method of ceramic heatersof a second and a third aspect of the present inventions.

[0062]FIG. 12 is an oblique view schematically showing gutters formedwhen a resistance heating element is subjected to trimming treatment.

[0063]FIG. 13 is a bottom plane view schematically showing oneembodiment of the ceramic heaters according to the second and the thirdaspect of the present invention.

[0064]FIG. 14 is an enlarged figure of a portion of the ceramic heatershown in FIG. 13.

[0065]FIG. 15 is a plane view schematically showing other ceramicheaters manufactured by the second and the third manufacturing methodsof the present invention.

[0066]FIG. 16(a) to (d) is a cross-sectional view schematically showinga portion of manufacturing process of the ceramic heater of the secondand the third aspect of the present inventions.

[0067]FIG. 17 is a chart showing the surface roughness of the resistanceheating element surface formed on the ceramic heater according toExample 14.

[0068]FIG. 18 is a chart showing the surface roughness of the conductorlayer surface formed on the ceramic substrate according to Example 15.

[0069] Explanation of Symbols  10, 20 a ceramic heater  11, 21 a ceramicsubstrate  11a, 21a a heating face  11b, 21b a bottom face  12, 22,(22a, 22b, 22c, 22d) a resistance heating element  13, 23 an externalterminal  14, 24 a bottomed hole  15, 25 a through hole  16 a lifter pin 17, 27 (27a, 27b, 27c, 27d) an insulating covering  19 a silicon wafer 110, 140 a ceramic heater  111, 141 a ceramic substrate  111a a heatingface  111b a bottom face  112 (112a to 112g), 142 (142a to 142d) aresistance heating element 1120 a metal covering layer 1130 a gutter 110 a laser trimming stage  110b a projection for fixation  110c astage  112m a conductor layer  114 a laser irradiating equipment  115 agalvanomirror  116 a motor  117 a control unit  118 a memory unit  119 acomputation unit  120 an input unit  121 a camera  133 an externalterminal  134, 44 a bottomed hole  135, 45 a through hole  136 a lifterpin  139 a silicon wafer

DETAILED DISCLOSURE OF THE INVENTION

[0070] At first, an embodiment of a ceramic heater of the first aspectof the present invention will be described with the reference offigures.

[0071]FIG. 1 is a bottom face view schematically showing one embodimentof a ceramic heater of the present invention and FIG. 2 is a partiallyenlarged figure of the above-mentioned ceramic heater.

[0072] The ceramic heater 10 comprises a disk-like ceramic substrate 11which is made of an insulating nitride ceramic or carbide ceramic.Approximately linear resistance heating elements 12, for example, inconcentrically circular state as shown in FIG. 1, are formed on one mainface of the ceramic substrate 11; and the other main face (hereinafter,referred to as a heating face) 11 a is made to be a face for: putting anobject to be heated such as a silicon wafer 19 thereon; or holding theobject at a given distance from the heating face 11 a to heat theobject.

[0073] As illustrated in FIG. 2, through holes 15 are formed in thevicinity of the center of the ceramic substrate 11 and lifter pins 16are inserted into the through holes 15 to support the silicon wafer 19.Also, at bottom faces 11 b, bottomed holes 14 to insert a temperaturemeasurement element such as a thermocouple into are formed.

[0074] In this ceramic heater 10, as illustrated in FIG. 2, aninsulating covering 17 with a given thickness and a surface roughness Raof the surface being 0.01 to 10 μm is formed on the surface part of theresistance heating element 12, so that the durability such as oxidationresistance, sulfurization resistance and the like is improved.Incidentally, in the ceramic heater 10, external terminals 13 areconnected to the terminal parts of the resistance heating element 12 andthe insulating covering 17 is formed also on a portion of the externalterminals 13. In such a case, generally, the insulating covering 17 isformed after the external terminals 13 are connected to the terminalparts of the resistance heating element 12.

[0075] In the case the insulating covering 17 is formed beforeconnection of the external terminals 13, the insulating covering 17cannot be formed at the portions where the external terminals 13 areconnected. Accordingly, in such a case, the portions at which theexternal terminals 13 are connected are generally not covered with theinsulating covering 17. Accordingly, after the connection of theexternal terminals 13, coating may be carried out again to form theinsulating covering 17 on the portions at which the external terminals13 are connected.

[0076] Conventionally, in the case of a heater including a resistanceheating element formed on the surface of a ceramic substrate, there isan disadvantageous point need to be improved such that heat is releasedfrom the exposed surface of the resistance heating element, andaccordingly the temperature of the heating face is not so raised for theapplied electric power, whereas in the present invention, since theinsulating covering 17 with a surface roughness Ra of 0.01 to 10 μm isformed, the heat diffusion from the resistance heating element 12 canappropriately be carried out.

[0077] That is, since the resistance heating element is covered with theinsulating covering having: the above-mentioned surface roughness; andproper thermal insulation effect, at the time of heating the ceramicsubstrate, heat is radiated at a high efficiency for the applied powerto keep a high surface temperature. Further, in the case a coolantexists in the surrounding, the roughened face formed on the insulatingcovering surface functions as a heat releasing fin, so that theresistance heating element can quickly be cooled and as a result, promptcooling of the ceramic heater can be achieved.

[0078] If the surface roughness Ra of the insulating covering surface isless than 0.01 μm, the thermal insulation effect is so significant thatefficient rise of the temperature is possible at the time of raising thetemperature of the ceramic substrate, however at the time of droppingthe temperature after heating of a silicon wafer and the like, thetemperature dropping speed of the resistance heating element is retardedand it is made impossible to repeat temperature rise and dropefficiently within a short time.

[0079] On the other hand, if the surface roughness Ra of the insulatingcovering surface exceeds 10 μm, air easily stagnates in valleys of theroughened surface and also since the thermal conductivity of theinsulating covering is low, the function as a heat insulation materialbecomes more significant than the effect as the heat releasing fin,making cooling efficiently within a short time impossible.

[0080] As the insulating covering 17, an oxide-based glass material oran electrically insulating synthetic resin (hereinafter, referred toheat resistant resin) having thermal resistance such as polyimide typeresin and silicone type resin can be employed. These materials may beused alone or in combination (in layered form and the like) of two ormore kinds of them. Incidentally, these materials will be describedlater.

[0081] Hereinafter, an instance of using aluminum nitride sintered bodysubstrate as a base material of the ceramic substrate is described,however the described base material is of course not limited to aluminumnitride and as the material examples, carbide ceramics, oxide ceramics,nitride ceramics other than aluminum nitride, and the like can beexemplified.

[0082] Examples of the above-mentioned carbide ceramics include, forexample, metal carbide ceramics such as silicon carbide, zirconiumcarbide, titanium carbide, tantalum carbide, and tungsten carbide andthe like, and examples of the above-mentioned oxide ceramics includesmetal oxide ceramics such as alumina, zirconia, cordielite, mullite andthe like. Further, examples of the above-mentioned nitride ceramicsinclude metal nitride ceramics such as aluminum nitride, siliconnitride, boron nitride, and titanium nitride and the like.

[0083] Among these ceramic materials, generally, nitride ceramics andcarbide ceramics have a higher thermal conductivity and therefore theyare more preferable than oxide ceramics. Incidentally, the materials ofthese materials for a sintered substrate may be used alone or incombination with two or more of them.

[0084] The ceramic heater comprising the nitride ceramics typicallyaluminum nitride and other carbide ceramics does not warp or strain byheating even if the thickness is thin because these ceramic materialshave a smaller thermal expansion coefficient than that of a metal andalso because ceramic materials have high rigidity. Thus, the heatersubstrate can be made thinner and lighter by weight than that made of ametal material such as aluminum and the like. Above all, since aluminumnitride is excellent in thermal conductivity, scarcely affected by lightand heat in a semiconductor producing device and excellent also incorrosion resistance to treatment gas, aluminum nitride can be employedpreferably as a heater material.

[0085] An insulating layer may be formed on the surface of the ceramicsubstrate comprising the above-mentioned nitride ceramics and carbideceramics.

[0086] That is because, in the case ceramic substrate itself has a highconductivity at a room temperature or a resistance thereof decreaseswhen the temperature thereof is in a high temperature region, if theresistance heating element is formed directly on the ceramic substratesurface, current leakage occurs between neighboring resistance heatingelement patterns and it results in incapability of functioning as aheater in some cases.

[0087] In this case, an insulating layer is to be formed on the ceramicsubstrate surface, then a resistance heating element is to be formed onthe insulating layer, and further an insulating covering is to be formedon the resistance heating element.

[0088] As the insulating layer, for example, an oxide ceramic is used.Such an oxide ceramic includes, for example, silica, alumina, mullite,cordielite, beryllia and the like. These oxide ceramics can be usedalone or in combination of two or more of them.

[0089] As a method for forming an insulating layer comprising thesematerials, for example, a method using a sol solution obtained byhydrolysis of alkoxides, forming a covering layer by spin coating andthe like and then drying and firing the covering layer. Further, theinsulating layer may be formed by CVD and sputtering and also theinsulating layer can be formed by applying a glass powder paste and thenfiring the paste at 500 to 1000° C.

[0090] The resistance heating element 12 is formed by forming aconductor containing paste layer in given patterns by applying aconductor containing paste containing metal particles of a noble metal(gold, silver, platinum, palladium), lead, tungsten, molybdenum, nickeland the like and then sintering the metal particles by baking. Thesintering of the metal particle is sufficient if the metal particles arefused to one another and the metal particles are stuck to the ceramicsubstrate. Incidentally, the resistance heating element 12 may be formedby using conductive ceramic particles of tungsten carbide, molybdenumcarbide and the like.

[0091] At the time of forming the resistance heating element 12, theresistance value can variously be set by controlling the shape (the linewidth and the thickness). Further, as being known well, if the width isadjusted to be narrower or the thickness is made thinner, the resistancevalue can be increased. The resistance heating element is in form ofapproximately linear or winding line with a certain width, however it isnot required to be strictly linear or winding from a geometric point ofview and may be in form of combination of straight lines and windinglines.

[0092] Since the oxide type glass material, which a material of theinsulating covering, has a high electric insulation property itself as amaterial and a high adhesion strength to the ceramic substrate and tothe resistance heating element and is chemically stable, it can form astable interface to the ceramic substrate and interface to theresistance heating element.

[0093] Examples of its practical composition includes, for example,ZnO—B₂O₃—SiO₂ which is containing ZnO as a main component, PbO—SiO₂,PbO—B₂O₃—SiO₂, and PbO—ZnO—B₂O₃ which are containing PbO as a maincomponent. These oxide type glass materials may have crystallineportions. The glass transition point of the glass material is 400 to700° C. and the thermal expansion coefficient is 4 to 9 ppm/° C.

[0094] As a method for forming the insulating covering of such oxidetype glass materials, a method for forming the insulating covering byapplying a paste containing the above-mentioned oxide type glass powderto the ceramic substrate surface by screen printing and drying andfiring can be exemplified. In this case, the portions where externalterminals are formed are required to be covered with a layer of resinrelatively easy to be decomposed at the time of heating so as to avoidthe formation of the insulating covering.

[0095] At that time, the surface roughness of the insulating coveringcan be adjusted by changing the drying condition (drying speed), firingcondition (firing temperature), or the average particle diameter of theglass powder. Further, the surface roughening may be carried out byforming the insulating covering and then carrying out sand blasttreatment of the surface.

[0096] Further, a heat resistant resin material, which is a material forthe insulating covering, also has an excellent electric insulationproperty and a high adhesion strength to the ceramic substrate and tothe resistance heating element. Further, use of the heat resistant resinmaterial makes formation of the insulating covering at a relatively lowtemperature possible. In the case of forming the insulating covering, itis only required to apply the material to the resistance heating elementsurface and dry and solidify the material, so that formation is easy andeconomical. Incidentally, the thermal resistance means that it can beused at a temperature of 150° C. or more and in such a case, nodeterioration of polymers and the like takes place.

[0097] Its practical examples include, for example, polyimide typeresin, silicone type resin and the like. The polyimide type resin ispolymer compounds obtained by the reaction of the carboxylic acidderivatives and diamines and has thermal resistance at 200° C. or moreand can be used in a wide temperature range. Further, the silicone typeresin comprises methyl and ethyl as an alkyl in the side chains ofpolysiloxanes and is excellent in thermal resistance and at the sametime has rubber elasticity, good adhesion property to the resistanceheating element and the ceramic substrate and is capable of forming theinsulating covering by being dried and solidified at a relatively lowtemperature, that is about 150 to 250° C.

[0098] As a method for forming an insulating covering comprising such aheat resistant resin material, a method comprising applying or sprayinga paste containing the above-mentioned heat resistant resin materialdissolved in a solvent and the like to the ceramic substrate surface anddrying the material can be exemplified.

[0099] In this case, the surface roughness of the insulating layer canbe adjusted by changing the drying condition (drying speed) and changingthe spraying condition and the like. Or, a roughened face may be formedby carrying out sand blast treatment of the surface or treatment using abelt sander after the formation of the insulating covering.

[0100] In this ceramic heater 10, the insulating covering 17 is formedon the surface portion of the resistance heating element 12 and thethickness of the insulating covering 17 is preferably 5 to 50 μm in thecase of the oxide glass and 10 to 50 μm in the case of the heatresistant resin.

[0101] That is because, in the ceramic heater 10, cooling is requiredafter heating in order to turn it to a normal temperature and if thethickness of the insulating covering 17 is too thick, cooling takes toolong, and consequently it results in productivity deterioration and onthe contrary, if it is too thin, the oxidation resistance of theresistance heating element is lowered and the temperature of the heatingface is lowered attributed to heat release from the exposed resistanceheating element surface.

[0102] As described above, if the insulating covering is formed on theresistance heating element surface, since these materials are excellentin the electric insulation property, it never occurs that electriccurrent leaks out of the insulating covering and flows and they canprotect the resistance heating element surface even in the case electricpower about 30 to 300 V is applied to the resistance heating element.

[0103] Further, the above-mentioned ceramic substrate has a high thermalconductivity and therefore can be formed to be thin in the thickness, sothat the surface temperature of the ceramic substrate can promptlyrespond to the temperature change of the resistance heating element andas a result, the ceramic heater 10 becomes excellent in temperaturecontrollability and the durability.

[0104]FIG. 3 is a bottom face view schematically showing anotherembodiment of a ceramic heater of the present invention and FIG. 4 is apartially enlarged cross-sectional view of the above-mentioned ceramicheater.

[0105] The ceramic heater 20 comprises a plate-like ceramic substrate21, similarly to the case of the ceramic heater 10 shown in FIG. 1. Theresistance heating elements 22 (22 a to 22 f) having approximatelylinear state concentrically as shown in FIG. 1 are formed on one mainface of the ceramic substrate 21 so as to form circuits; and the othermain face thereof is made to be a face to put an object to be heatedthereon or sustain it to heat the object.

[0106] Further, in the ceramic heater 20, the insulating coverings areformed on a stretch of area containing a portion on which theabove-mentioned circuits are formed. That is, around the resistanceheating element 22 a, 22 b, 22 c at which the circuits are kept atrelatively wide distances from one another, the insulating covering 27a, 27 b, 27 c are formed on a stretch of area containing a portion onwhich the above-mentioned circuits are formed and the surroundingsthereof, on the other hand, around the resistance heating elements 22 d,22 e, 22 f which are kept at narrow gaps from one another, theinsulating covering 27 d is formed on the entire area comprising: theareas sandwiched between the neighboring resistance heating elementsconstituting the circuits; their surrounding areas; and the areasbetween the respective neighboring circuits.

[0107] In the ceramic heater 20 with such a constitution, the sameeffect as that of the case of the ceramic heater 10 shown in FIG. 1 isprovided and occurrence of short-circuit between neighboring circuitsowing to migration of a metal particle (for example, silver particle)contained in the resistance heating element 22 can be prevented.Further, at the time of forming the insulating covering 27, theinsulating covering 27 can be formed by forming a covering layer in agiven area by screen printing and the like and heating the coveringlayer, so that the insulating covering can relatively easily andefficiently be formed and the covering cost is lowered to result in aneconomical heater.

[0108] As the insulating covering 17 similar to the case of the ceramicheater shown in FIG. 1, either an oxide type glass material or heatresistant resin of such as polyimide type resin, silicone type resin canbe employed.

[0109] Further, similar to the case of the ceramic heater shown in FIG.1, as the material of the base material of the ceramic substrate, forexample, carbide ceramics, oxide ceramics, nitride ceramics and the likecan be employed.

[0110] Also, for the material of the resistance heating element 22,similar materials to those in the case of the ceramic heater 10 shown inFIG. 1 can be used and the resistance heating element 22 can be formedby a similar method to that in the case of the ceramic heater 10 shownin FIG. 1.

[0111] In the ceramic heater 20, the thickness of the insulatingcovering 27 (the thickness from the surface of the resistance heatingelement 22) is preferably same as that in the case of the ceramic heater10 shown in FIG. 1 and the thickness from the bottom face of the ceramicsubstrate 21 at the portion where no resistance heating element 22 isformed is preferably 10 to 50 μm in the case of oxide glass and 10 to 50μm in the case of heat resistant resin.

[0112]FIG. 5 is a bottom face figure schematically showing furtheranother embodiment of the ceramic heater of the present invention.

[0113] The ceramic heater 30 has the same structure as that of theceramic heater 20 except that an insulating covering 37 is formed in theentire area where the resistance heating element 22 of theabove-mentioned ceramic heater 20 is formed and the same effect as thatof the ceramic heater 10 shown in FIG. 1 is provided and besides,occurrence of short-circuit and the like in the resistance heatingelement owing to the migration of a metal (for example, silver and thelike) constituting the resistance heating element 22 can be prevented.Further, also in the case of forming the insulating covering 37, it caneasily and effectively be formed because a coating layer is formed byscreen printing and the like and the insulating covering 37 is formed bya heating it and the like, to result in a decrease of a covering costand cost down of the heater.

[0114] As described above, the insulating covering in the presentinvention may include those having a variety of covering structures suchas: the structure of covering only on the surface of circuits; thestructure of covering a stretch of area containing a portion on whichthe circuits are formed: the structure of integrally covering two ormore neighboring circuits in the diameter direction of the ceramicsubstrate in a lump; the structure of covering the whole area where thecircuits are formed; and the like.

[0115] Practical examples of the ceramic heater of the first aspect ofthe present invention with such a constitution and their manufacturingmethod will be described as the best mode for carrying out the presentinvention later. Of course, the practical examples and the manufacturingmethod to be described later are only examples and the ceramic heater ofthe first aspect of the present invention is not limited only to theseexamples and the manufacturing method at all.

[0116] Next, manufacturing methods of ceramic heaters of the second andthe third aspect of the present invention will be described.

[0117] The manufacturing method of a ceramic heater of the second aspectof the present invention is a ceramic heater manufacturing methodcomprising the steps of: forming a resistance heating element having agiven pattern on a surf ace of a ceramic substrate; and irradiatinglaser beam onto the resistance heating element to form a gutter or a cutafter the preceding step so as to adjust a resistance value of theresistance heating element, wherein when the resistance heating elementis formed on the surface of the ceramic substrate, a surface roughnessRa of the resistance heating element is 0.01 μm or more in accordancewith JIS B 0601.

[0118] The manufacturing method of a ceramic heater of the third aspectof the present invention is a ceramic heater manufacturing methodcomprising the steps of: forming a strip-shaped or a ring-shapedconductor layer on a given area of a surface of a ceramic substrate; andirradiating laser beam onto the conductor layer to remove a part of theconductor layer by performing trimming after the preceding step so as toform a resistance heating element having a given pattern, wherein whenthe conductor layer is formed on the surface of the ceramic substrate, asurface roughness Ra of the conductor layer is 0.01 μm or more inaccordance with JIS B 0601.

[0119] There is a difference between both inventions: in the secondaspect of the present invention, the resistance value of the resistanceheating element is adjusted by performing trimming the resistanceheating element formed in given patterns, whereas in the third aspect ofthe present invention, some portions of the above-mentioned conductorlayer are removed by laser beam irradiation to form the resistanceheating element patterns.

[0120] However, both inventions are in common in the point that laserbeam is irradiated to a specified area of the ceramic substrate and theirradiated portions of the conductor layer (the resistance heatingelement) are removed and the same laser trimming equipment can beemployed.

[0121] Accordingly, hereinafter, except the cases separate descriptionsare necessary, the above-mentioned two inventions will be described inparallel.

[0122] At first, in the manufacturing methods of the second and thethird aspect of the present inventions, the trimming method to beemployed at the time of performing laser trimming will be described andsuccessively the laser trimming using the equipment will be described.

[0123]FIG. 11 is a block diagram showing the outline of the lasertrimming equipment to be employed for the manufacturing methods of thesecond and the third aspect of the present inventions.

[0124] At the time of performing laser trimming, as shown in FIG. 11, aceramic substrate 111 on which either a conductor layer 112 m is formedin concentric circles (ring shapes) with a given width so as to includethe circuits of the resistance heating element to be formed or aresistance heating element with given patterns are formed is fixed on astage 110 c.

[0125] On the stage 110 c, a motor or the like (not illustrated) isinstalled and is connected to a control unit 117 and the motor or thelike is driven by signals from the control unit 117 to make it possibleto freely move the stage 110 c in the θ direction (the turning directionof the ceramic substrate) and x-y directions.

[0126] On the other hand, above the stage 110 c, a galvanomirror 115 isinstalled and the angle of the galvanomirror 115 is made freelychangeable in the x-direction by the motor 116. The laser beam 122irradiated from a laser irradiating equipment 114 installed also abovethe stage 10 c comes into collision against the galvanomirror 115 andreflected thereon so as to irradiate the ceramic substrate 111.

[0127] Further, the motor 116 and the laser irradiating equipment 114are connected to the control unit 117 and by the signals from thecontrol unit 117, the motor 116 and the laser irradiating equipment 114are driven so as to turn the galvanomirror at a given angle around theaxis in the x-direction. Also, a motor (not illustrated) installed inthe stage 110 c is driven by signals from the control unit 117 to turnthe table in the θ-direction. Owing to the turning of the galvanomirroraround the axis in the x-direction and the turning of the table in theθ-direction, the irradiation position of the ceramic substrate 111 canfreely be set.

[0128] Incidentally, the table is able to turn not only in theθ-direction but also move in the x-y direction.

[0129] In such a manner, the stage 110 c on which the ceramic substrate111 is put and/or the galvanomirror 115 is moved, so that the laser beam122 can be irradiated to any optional position of the ceramic substrate111.

[0130] On the other hand, a camera 121 is also installed above the stage110 c and consequently, the position (x, y) of the ceramic substrate 111is made recognizable. The camera 121 is connected to a memory unit 118and accordingly the position (x, y) of the conductor layer 112 m of theceramic substrate 111 is recognized and laser beam 122 is irradiated tothe position.

[0131] Further, an input unit 120 is connected to the memory unit 118and comprises a keyboard (not illustrated) as a terminal and through thememory unit 118 and the keyboard and the like, given instructions areinputted.

[0132] Further, the laser trimming equipment is provided with acomputation unit 119 and based on the data of such as the position ofthe ceramic substrate 111 recognized by the camera 121 and the thicknessof the resistance heating element, computation for controlling theirradiation position, the irradiation speed, the intensity of the laserbeam 122 is carried out and based on the computation results,instructions are transmitted to the motor 116, laser irradiationequipment 114 and the like from the control unit 117 to irradiate laserbeam 122 while turning the galvanomirror 115 or moving or turning thestage 110 c in order to perform trimming of the unnecessary portions ofthe conductor layer 112 m.

[0133] Further, the laser trimming equipment comprises a resistivitymeasuring unit 123. The resistivity measuring unit 123 is provided witha plurality of tester pins 124. After dividing the resistance heatingelement into a plurality of sections, the tester pins 124 are broughtinto contact with the respective sections so as to measure theresistance value of the formed resistance heating element patterns.Then, based on the measured resistance value, laser is irradiated to thesections where the resistance value is low: to form gutters (referenceto FIG. 12) approximately parallel to the electric current flowdirection of the resistance heating element; or to form cutsapproximately perpendicular to the electric current flow direction, sothat the resistance value of the resistance heating element is adjustedand the resistance heating element with little unevenness of theresistance value can be obtained.

[0134] Next, a trimming method using such a laser trimming equipmentwill be described specifically.

[0135] In this case, a method for forming a resistance heating elementby removing unnecessary portions of a strip-shaped or a ring shapedconductor layer which is formed on a ceramic substrate will mainly bedescribed and a method for adjusting the resistance value of theresistance heating element will be described later.

[0136] Further, the steps other than the laser trimming step in themanufacturing methods of the ceramic heaters of the second and the thirdaspect of the present invention will be described in details later andhere the steps will briefly described.

[0137] At first, a ceramic substrate is manufactured. In this process,firstly, a raw formed body comprising a ceramic powder and resin isproduced. There are two production method of the raw formed body: one isa production method including the steps of producing a granulecontaining the ceramic powder and the resin and then loading a die orthe like with the granule, and applying pressing pressure thereto; andthe other is a production method including the steps of laminating andpressure-bonding green sheets. Proper methods will be selected dependingon whether another conductor layer of electrostatic electrodes and thelike will be formed in the inside or not and the like. After that,degreasing and firing of the raw formed body is carried out tomanufacture the ceramic substrate.

[0138] After that, through holes are formed in the ceramic substrate toinsert lifter pins and bottomed holes are formed to bury temperaturemeasurement elements.

[0139] Next, to a wide area including the portions which is subjected tobe the resistance heating elements on the ceramic substrate 111, aconductor containing paste layer with a shape as shown in FIG. 11 isformed by screen printing and the like and after that, a conductorcontaining paste layer is fired to form the conductor layer 112 m.

[0140] The conductor layer may be formed by employing a plating method,a physical deposition method such as a sputtering. In the case ofplating, a plating resist is formed and in the case of sputtering,selective etching is carried out, so that the conductor layer 112 m canbe formed in the given area.

[0141] Further, the conductor layer may be formed as described above ina manner some portions of the conductor layer are formed as resistanceheating element patterns.

[0142] At the time of forming the conductor layer, the surface roughnessRa of the above-mentioned conductor layer according to JIS B 0601 isadjusted to 0.01 μm or more, preferably 0.1 to 10 μm. A method forforming a conductor layer (a resistance heating element) having such aroughened face will be described in details later and in the case offorming the conductor layer by screen printing, the surface roughness ofthe conductor layer can be adjusted by selecting the shape and theaverage particle diameter of a metal particle to be employed as a rawmaterial for the resistance heating element. Further, at the time offorming the conductor layer by plating, for example, if conditions underwhich an acicular crystal is precipitated is selected to carry out theplating, the surface roughness can be adjusted. Further, buff grinding,sand blast treatment is also capable of adjusting the surface roughness.

[0143] Next, as shown in FIG. 14, projections 110 b for fixation formedin the stage 110 c and to be brought into contact with side faces of theceramic substrate 111 and projections (not illustrated) for fitting tobe fit in through holes to insert lifter pins into are used to fix theceramic substrate 111 on the stage 110 c.

[0144] Further, data of the resistance heating element patterns ispreviously inputted through the input unit 120 and housed in the memoryunit 118. That is, the data of the resistance heating element patternsto be formed by performing trimming is stored. The data of theresistance heating element patterns is the data to be used for formingthe resistance heating element patterns by performing trimming theconductor layer printed like a plane (so-called spread state or ringshaped).

[0145] Next, the fixed ceramic substrate 111 is photographed by thecamera 121, so that the formation position of the conductor layer 112 mis stored in the memory unit 118.

[0146] Based on the data of the position of the conductor layer,computation is carried out in the computation unit 119 and the resultsare stored in the memory unit 118 as the control data.

[0147] After that, based on the computation results, the control signalsare generated from the control unit 117 and while the motor 116 of thegalvanomirror 115 and/or the motor of the stage 110 c being driven, alaser beam is irradiated to trim unnecessary portions of the conductorlayer 112 m with the surface roughness of 0.01 μm or more and theresistance heating element 112 is formed.

[0148] At the time of removing the unnecessary portions of the conductorlayer and the like in such a manner, it is important that even thoughthe portions of the conductor layer and the like which should be trimmedby the laser beam irradiation are trimmed, the laser beam does notaffect the ceramic substrate existing thereunder.

[0149] Accordingly, the laser beam is required to be selected so as tobe well absorbed in the metal particle and the like constituting theconductor layer and the like, on the other hand, be hardly absorbed inthe ceramic substrate. Such laser type includes, YAG laser, carbonicacid gas laser, excimer (KrF) laser, UV (ultraviolet) laser and thelike.

[0150] Among them, YAG laser and excimer (KrF) laser are the mostoptimum.

[0151] As YAG laser, SL 432H, SL 436G, SL 432GT, SL 411B and the likemanufactured by NEC can be employed.

[0152] As laser, pulsed beam with a frequency of 2 kHz or less ispreferable and pulsed beam with a frequency of 1 kHz or less is morepreferable. It is because high energy can be irradiated to theresistance heating element within an extremely short time and the damageon the ceramic substrate can be suppressed to slight. Further, theenergy of the first pulse does not become high and gutters with a widthas designed can be formed. If the frequency of the pulses of the laserbeam exceeds 2 KHz, the energy of the first pulse becomes too high andthe gutters with a wider width than designed are formed andconsequently, the resistance heating element cannot be formed asdesigned.

[0153] Further, the processing speed is preferably 100 mm/second orless. It is because if it exceeds 100 mm/second, gutters cannot beformed unless the frequency is increased. As described above, in orderto limit the frequency up to 2 kHz, the speed is preferably 100mm/second or less.

[0154] The output of the laser is preferably 0.3 W or more. It isbecause if it is less than 0.3 W, the conductor layer to be removed forforming the patterns of the resistance heating element may notcompletely trimmed in some cases. Especially, in the case the resistanceheating element is of a sintered body of a metal particle, trimming withthe output of 0.3 W or more can be carried out to the depth reaching theceramic substrate and makes complete removal of the conductor layerpossible.

[0155] Although trimming may be carried out for the conductor containingpaste layer, trimming is preferable to be performed after formation ofthe conductor layer, as described above, after printing a conductorcontaining paste and then firing the printed paste. It is because: theresistance value is fluctuated by firing the paste; and the paste maypossibly be peeled in some cases attributed to irradiation of the laserbeam.

[0156] The manufacturing method of the second and the third aspect ofthe present inventions is a method of forming a ring shaped (so-calledspread state) paste by using a conductor containing paste and performingtrimming the formed paste so as to pattern it. Hence, heating elementpatterns with an even thickness can be obtained. If the printing of theheating element patterns is conducted from the beginning, the thicknessbecomes uneven depending on the printing direction so that it becomesdifficult to form the resistance heating element with an even thickness.

[0157] In the above-mentioned description, the method for forming theresistance heating element by laser beam irradiation was described, butin the case of adjusting the resistance value of the resistance heatingelement by performing trimming after formation of the resistance heatingelement in the given patterns on the ceramic substrate, as shown in FIG.12, gutters 1130 are formed in approximately parallel to the directionof the electric current flow in the resistance heating element 112 andthereby, the resistance value of the resistance heating element can beadjusted. Although the resistance may be adjusted by forming cutsapproximately perpendicularly to the direction of the electric currentflow in the resistance heating element, the method for forming guttersis preferable since it is less probable to cause disconnection of theheating element.

[0158] In this case, as described above, the resistance heating elementis divided into a large number of the portions and using tester pins124, the resistance values of the respectively divided portions aremeasured and their resistance values are adjusted by performingtrimming.

[0159] The patterns of the resistance heating element formed by suchlaser trimming is not particularly limited and, for example, thefollowing resistance heating element patterns can be exemplified.Incidentally, hereinafter, the ceramic heater comprising the resistanceheating element patterns will be shown.

[0160]FIG. 13 is a bottom face view schematically showing the ceramicheater manufactured by the ceramic heater manufacturing method of thesecond aspect of the present invention and FIG. 14 is a partiallyenlarged cross-sectional view of the ceramic heater. Incidentally,gutters formed by performing trimming are not shown in the resistanceheating element patterns 112 a to 112 g shown in FIG. 14.

[0161] The ceramic heater 110 has the resistance heating element 112(112 a to 112 g) on the bottom face 111 b, the reverse side of theheating face 111 a of the ceramic substrate 111 formed into a disk-likeshape.

[0162] The resistance heating element 112 is formed into patternscomposed of basically arcs so repeated as to draw a part of concentriccircles in order to carry out heating in a manner that the entire areaof the heating face 111 a has an even temperature.

[0163] That is, the resistance heating element patterns 112 a to 112 dwhich are closest to outer circumference are formed by repeatingpatterns in an arc-like shape formed by dividing respective concentriccircles into four and the end parts of the neighboring arcs areconnected to each other through winding lines to form series ofcircuits. Four circuits comprising such resistance heating elementpatterns 112 a to 112 d are arranged near to one another so as to besurrounded by the outer circumference to form ring-shaped patterns as awhole.

[0164] Further, the end parts of the circuits composed of the resistanceheating element patterns 112 a to 112 d are formed in the inside of thering-shaped patterns in order to prevent formation of cooling spots andsubsequently, the end parts of the circuits in the outer side areextended toward the inside.

[0165] Inside of the resistance heating element patterns 112 a to 112 dformed in the periphery, the resistance heating element patterns 112 e,112 f, and 112 g respectively composed of concentrically patternedcircuits of which slight portions are cut are formed and in theresistance heating element patterns 112 e, 112 f, and 112 g, end partsof the neighboring concentric circles are connected to each othersuccessively through the resistance heating element patterns of straightlines to form series of circuits.

[0166] Further, in the spaces between respectively neighboringresistance heating element patterns 112 a to 112 d, 112 e, 112 f, and112 g, belt-like (ring-shaped) no-resistance heating element formed areaare formed and also in the center part, no-resistance heating elementformed area is formed.

[0167] Accordingly, as a whole view, the ring-shaped resistance heatingelement formed area and no-resistance heating element formed area arealternately formed from the outer side to the inner side and inconsideration of the size (the diameter) and the thickness of theceramic substrate, these areas are properly designed, so that it is madepossible to make the temperature of the heating face even.

[0168] After trimming treatment, the resistance heating element patterns112 a to 112 g are covered with a metal covering layer 1120 asillustrated in FIG. 14 in order to prevent corrosion and externalterminals 133 are connected to their end parts through the solder layer1120.

[0169] In the ceramic substrate 111, three through holes 135 are formedat the positions in the no-resistance heating element formed area andother than the case that an object to be heated, such as a silicon wafer139, is heated while being put directly on the heating face 111 a of theceramic substrate 111, the object to be heated can be heated while beingkept at a given distance from the ceramic substrate 111 by insertinglifter pins 136 into these through holes 135 and holding the object tobe heated such as a silicon wafer 139 by the lifter pins 136 asillustrate in FIG. 14.

[0170] Further, it is also made possible to receive an object to beheated such as the silicon wafer 139 from a transporting equipment, putthe object on the ceramic substrate 111, and to heat the object to beheated while being supported. Concave portions are formed in the heatingface 111 a of the ceramic substrate 111 and supporting pins are arrangedin the concave portions so as to be slightly projected out of theheating face 111 a and the silicon wafer 139 can be heated while beingkept at 5 to 5,000 μm from the heating face of the silicon wafer 139 bysupporting the silicon wafer 139 by the supporting pins.

[0171] In the no-resistance heating element formed area on the bottomface 111 b of the ceramic substrate 111, bottomed holes 134 are formedand in the bottomed holes 134, temperature measurement elements 137 suchas thermocouples are inserted and it is made possible to measure thetemperature in the vicinity of the heating face 111 a of the ceramicsubstrate 111.

[0172] In the ceramic heater having the above-mentioned resistanceheating element patterns, the resistance heating element is composed of:the patterns forming series of circuits by combining arcs and windinglines repeatedly formed as if drawing some portions of concentriccircles on the disk-like ceramic substrate (hereinafter, referred alsoto as arc-repeated patterns); and the patterns composed of series ofcircuits formed by straightly connecting end parts of the neighboringconcentric circles of which small portions are cut (hereinafter referredalso to as concentric circles-like patterns), thus, most portions ofsuch resistance heating element patterns can be defined with distance rfrom the center of the ceramic substrate and the rotation angle (θ₁-θ₂).

[0173] Accordingly, at the time of performing laser trimming, if theceramic substrate is mainly rotated around its center, the resistancevalue of the resistance heating element can relatively easily beadjusted and in the ceramic heater comprising the resistance heatingelement whose resistance value is adjusted by such a method, thetemperature of the heating face becomes even and an object to be heatedsuch as a semiconductor wafer can be heated at an even temperature.

[0174] Further, by the manufacturing method of the third aspect of thepresent invention, that is, by performing trimming of the conductorlayer of the ceramic heater formed in ring shape, the ceramic heaterhaving the resistance heating element in patterns shown in FIG. 13 canbe manufactured. That is the same in the case of a ceramic heater havingthe resistance heating element with the shape described below.

[0175] The ceramic heater to be manufactured by the manufacturing methodof the second and the third aspect of the present inventions is notlimited to those having the resistance heating element in patterns shownin FIG. 13 and may have: the above-mentioned arc-repeated patterns;concentric circles-like patterns and repeated pattern of winding lines,alone or in combination of these patterns arbitrarily.

[0176]FIG. 15 is a plane view schematically showing another embodimentof the ceramic heater to be manufactured by the manufacturing methods ofthe second and the third aspect of the present inventions. In theceramic heater, as shown in FIG. 15, resistance heating element patterns142 a, 142 b, 142 c mainly composed of winding lines and respectivelyformed in a ring shapes are arranged in a radiating manner as a whole soas to sandwich the circular no-resistance heating element formed areaand the center no-resistance heating element formed area.

[0177] Incidentally, as illustrated in FIGS. 13, 15, the resistanceheating element formed on the surface of the ceramic substrate ispreferable to be divided into two or more circuits. Owing to thedivision of the circuits, the calorific value can be controlled byelectric power to be applied to the respective circuits and thus, thetemperature of the heating face of the silicon wafer can be controlled.

[0178] At the time of forming such resistance heating element patterns,in the case the patterns have wide gaps between neighboring resistanceheating element patterns as shown in FIG. 15, the resistance heatingelement can easily be formed by screen printing. Whereas, in the casethe patterns have the narrow gaps and complicated (dense) shape as shownin FIG. 13, by a method comprising steps of at first forming aring-shaped conductor layer composed of wide strip-shaped lines and thenperforming trimming the parts (unnecessary parts) where resistanceheating element is not supposed to exist by laser beam, the resistanceheating element can be relatively easily formed and thereforeadvantageous.

[0179] In the case of forming the resistance heating element on thesurface of the ceramic substrate, the thickness of the resistanceheating element is preferably 1 to 30 μm and more preferably 1 to 10 μm.The width of the resistance heating element is preferably 0.1 to 20 mmand more preferably 0.1 to 5 mm.

[0180] The resistance value of the resistance heating element can bechanged by the width and the thickness, and the above-mentioned rangesare most practical.

[0181] The resistance heating element may have a cross-sectional shapewith either a rectangular or an elliptical shape, however it ispreferably flat. It is because if the shape is flat, heat irradiationtoward the heating face easily takes place and uneven temperaturedistribution in the heating face is hardly caused.

[0182] The aspect ratio of the cross-section (width of the resistanceheating element/thickness of the resistance heating element) ispreferably 10 to 5000.

[0183] It is because the resistance value of the resistance heatingelement can be high and the evenness of the temperature in the heatingface can be assured as well by controlling the ratio within the range.

[0184] In the case of making the thickness of the resistance heatingelement constant, if the aspect ratio is smaller than theabove-mentioned range, the transmission quantity of the heat in theheating face direction in the ceramic substrate is lowered and thetemperature distribution similar to the patterns of the resistanceheating element is caused in the heating face and on the contrary, theaspect ratio is too high, the portions immediately above the center ofthe resistance heating element becomes at high temperature andconsequently, temperature distribution similar to the patterns of theresistance heating element is caused in the heating face. Accordingly,taking the temperature distribution into consideration, the aspect ratioof the cross-section is preferably 10 to 5000.

[0185] Regarding the dispersion of the resistance value of theresistance heating element, the dispersion of the resistance value inrelation to the average resistance value is preferably 5% or less andmore preferably 1%. The resistance heating element of the presentinvention is divided into a plurality of circuits, and keeping theresistance value dispersion small as described above makes it possibleto decrease the number of the division of the resistance heating elementand makes it easy to control the temperature. Further, the temperatureof the heating face during the transition period of temperature rise canbecome even.

[0186] Generally, such a resistance heating element is formed byapplying to the ceramic substrate a conductor containing pastecontaining a metal particle and a conductive ceramic particle forensuring the conductivity and firing the paste. The conductor containingpaste is not particularly limited, however those containing resin, asolvent, and a thickening agent other than the above-mentioned metalparticle or the conductive ceramic are preferable.

[0187] As the above-mentioned metal particle, for example, a noble metal(gold, silver, platinum, palladium), lead, tungsten, molybdenum, nickeland the like are preferable. They may be used alone or in combination oftwo or more of them. Because these metals are relatively hard to beoxidized and have sufficient resistance value enough to generate heat.

[0188] As the above-mentioned conductive ceramic, for example, carbideof tungsten and molybdenum can be exemplified. They may be used alone orin combination of two or more of them.

[0189] The particle diameter of the metal particle or the conductiveceramic particle is preferably 1 to 100 μm. It is because if it is toosmall, less than 1 μm, the surface roughness Ra of the resistanceheating element easily becomes less than 0.01 μm and at the time ofperforming trimming by laser beam irradiation, laser beam is easy to bereflected and gutters cannot be formed as designed and on the otherhand, if the particle diameter of the metal particle and the likeexceeds 100 μm, sintering becomes hard to be carried out to result in ahigh resistance value.

[0190] The shape of the above-mentioned metal particle may be sphericalor scaly, however it is more preferably spherical. It is because thesurface roughness of the resistance heating element can be more easilyroughened. Further, even in the case of scaly shape, if the aspect ratio(the width or length/the thickness) is not so high, the surfaceroughness can be made high because the particle is disposed easilyperpendicularly or slantingly in relation to the formation face of theresistance heating element.

[0191] In the case of using such a metal particle, a mixture of theabove-mentioned spherical particle and the above-mentioned scalyparticle can be used.

[0192] In the case the above-mentioned metal particle is a spherical oneor a mixture of the spherical one and the scaly one, the metal oxide caneasily be held among the metal particle and the adhesion strengthbetween the resistance heating element and the nitride ceramic and thelike can be assured and the resistance value can be high and thereforethey are advantageous.

[0193] Further, in the case of an ascicular particle, if it has anaspect ratio (the length in relation to the diameter) not so high, theparticle is disposed easily perpendicularly or slantingly in relation tothe formed face of the resistance heating element, so that the surfaceroughness can be high.

[0194] As the resin to be used for the conductor containing paste, forexample, epoxy resin, phenol resin and the like can be exemplified.Also, as the solvent, for example, isopropyl alcohol and the like can beexemplified. As the thickening agent, cellulose and the like can beexemplified.

[0195] As the conductor containing paste, one containing a metalparticle added with a metal oxide is used and it is preferable to sinterthe metal particle and the metal oxide after application to the ceramicsubstrate. Because sintering of the metal oxide together with the metalparticle makes the adhesion of the metal particle and the nitrideceramic of the ceramic substrate further close.

[0196] The reason for the improvement of the adhesion to the nitrideceramic and the like owing to the metal oxide addition is not madeclear, however it can be supposed that the metal particle surface andthe surface of the nitride ceramic and the like are slightly oxidizedand covered with an oxide film and the respective oxide films areunitedly sintered through the metal oxide to cause close adhesionbetween the metal particle and the nitride ceramic. Further, in the casethe ceramic of the ceramic substrate is an oxide, since the surface isnaturally the oxide, a conductor layer with a high adhesion strength canbe formed.

[0197] As the above-mentioned metal oxide, for example, at least oneoxide selected from a group consisting of lead oxide, zinc oxide,silica, boron oxide (B₂O₃), alumina, yttria, and titania is preferableto be used.

[0198] It is because these oxides can improve the adhesion strength tothe metal particle and the nitride ceramic without increasing theresistance value of the resistance heating element 112.

[0199] The ratio of the above-mentioned lead oxide, zinc oxide, silica,boron oxide (B₂O₃), alumina, yttria, and titania is respectively 1 to 10for lead oxide, 1 to 30 for silica, 5 to 50 for boron oxide, 20 to 70for zinc oxide, 1 to 10 for alumina, 1 to 50 for yttria, 1 to 50 fortitania by weight ratio in the case the total amount of the metal oxidesis set to be 100 parts by weight and they are preferable to be adjustedso as to keep their total not exceeding 100 parts by weight.

[0200] Adjustment of the quantities of these oxides in these ranges isefficient to improve the adhesion property especially to the nitrideceramic.

[0201] The addition amount of the above-mentioned metal oxides inrelation to the metal particle is preferably not less than 0.1% byweight and less than 10% by weight. Further, the area resistivity in thecase the resistance heating element 12 is formed using such a conductorcontaining paste is preferably 1 to 45 mΩ/

.

[0202] If the area resistivity exceeds 45 mΩ/

, the calorific value for the applied voltage becomes too high and inthe case of a ceramic substrate 11 bearing the resistance heatingelement 12 on the surface, the calorific value becomes difficult to becontrolled. If the addition amount of the metal oxides is 10% by weightor more, the area resistivity exceeds 50 mΩ/

and the calorific value becomes too high to control the temperature andconsequently, the evenness of the temperature distribution deteriorates.

[0203] Further, if necessary, the area resistivity can be controlled tobe 50 mΩ/

to 10 Ω/

. If the area resistivity is increased, the pattern width can be wideand there occurs no disconnection problem.

[0204] In the case the resistance heating element is formed on thesurface of the ceramic substrate, a metal covering layer is preferableto be formed on the surface part of the resistance heating element. Itis because the resistance value change owing to oxidation of the metalsintered body in the inside can be prevented. The thickness of the metalcovering layer to be formed is preferably 0.1 to 10 μm. Such a metalcovering layer is to be formed after the above-mentioned trimmingtreatment is performed.

[0205] The metal to be used for the metal covering layer formation isnot particularly limited if it is a non-oxidizable metal andpractically, for example, gold, silver, palladium, platinum, nickel andthe like can be exemplified. They can be used alone or in combination oftwo or more of them. Among them, nickel is preferable.

[0206] It is because, for the resistance heating element, terminals forthe connection to an electric power are required to be attached to theresistance heating element through a solder because nickel can preventthermal diffusion of the solder. As the connection terminals, those madeof Kovar can be exemplified.

[0207] The ceramic substrate to be used for manufacturing methods of thesecond and the third aspect of the present inventions is preferably adisk plate and those with a diameter exceeding 190 mm are preferable.Because such a substrate with a larger diameter has a wider temperaturedispersion on the heating surface.

[0208] The thickness of the above-mentioned ceramic substrate ispreferably 25 mm or less. Because, if the thickness of theabove-mentioned ceramic substrate exceeds 25 mm, thetemperature-following property deteriorates.

[0209] The thickness is more preferably not exceeding 1.5 mm and 5 mm orless. Because if the thickness is thicker than 5 mm, the heattransmission becomes difficult and the heating efficiency tends todeteriorate, whereas if it is 1.5 mm or less, the heat transmitted inthe ceramic substrate is not sufficiently diffused, so that thetemperature distribution possibly becomes uneven in the heating face andthe strength of the ceramic substrate is possibly deteriorated andbroken.

[0210] In the ceramic heater 110 manufactured by the manufacturingmethods of the second and the third aspect of the present inventions, aceramic is used as the material of the substrate, however the materialof the ceramic is not particularly limited and, for example, a nitrideceramic, a carbide ceramic, and an oxide ceramic can be exemplified.

[0211] As the material for the ceramic substrate 111, among thempreferable are the nitride ceramic and the carbide ceramic. Because theyare excellent in the thermal conduction.

[0212] The above-mentioned nitride ceramic includes, for example,aluminum nitride, silicon nitride, boron nitride, titanium nitride, andthe like. Also, the above-mentioned carbide ceramic includes siliconcarbide, titanium carbide, boron carbide and the like. Further, as theabove-mentioned oxide ceramic, the example thereof include alumina,cordierite, mullite, silica, beryllia and the like. They may be usedalone or in combination of two or more of them.

[0213] Among them, the most preferable is aluminum nitride. Because ithas the highest thermal conduction of 180 W/m·K.

[0214] However, a material which hardly absorbs laser beam is preferablefor the ceramic substrate 111 and for example, in the case of thealuminum nitride substrate, those having a carbon content of 5000 ppm orless are preferable.

[0215] Further, the surface roughness is preferably made to have Ra of20 μm or less according to JIS B 0601 by grinding the surface. Becausein the case the surface roughness is high, laser beam is absorbed.

[0216] Further, if necessary, a heat resistant ceramic layer may beformed between the resistance heating element and the ceramic substrate.For example, in the case of a non-oxide type ceramic, an oxide ceramicmay be formed on the surface.

[0217] The method for forming the resistance heating element on thesurface of the ceramic substrate, using the above-mentioned method,includes: a method for forming the resistance heating element patternsby applying a conductor containing paste in a plane shape (a ring likeshape) to a given area of the ceramic substrate and then performinglaser trimming to form a resistance heating element; and a method forforming a resistance heating element in given patterns by baking aconductor containing paste and then performing laser trimming to form aresistance heating element. Among these method, a method involving stepsof baking the conductor containing paste on and then forming theresistance heating element patterns is preferable since peeling of theconductor containing paste layer and the like is not caused by laserbeam irradiation.

[0218] Incidentally, the sintering of metal is sufficient if the metalparticles are melted and adhered to each other and the metal particlesand the ceramic are melted and adhered to each other. Further, theresistance heating element patterns may be formed by forming theconductor layer in given areas by employing a method of such as aplating and a sputtering and then performing laser trimming.

[0219] Next, the ceramic heater manufacturing methods of the second andthe third aspect of the present inventions other than theabove-mentioned laser trimming step will be described with reference toFIG. 16.

[0220] FIGS. 16(a) to 16(d) shows cross-sectional view schematicallyillustrating some portion of the ceramic heater manufacturing methods ofthe second and the third aspect of the present inventions including thelaser treatment.

[0221] (1) Ceramic Substrate Manufacturing Step

[0222] After a slurry is produced by mixing a sintering aid such asyttria (Y₂O₃), a compound containing Na and Ca, and a binder based onthe necessity with a ceramic powder of such as aluminum nitride and theslurry is granulated by spray drying method and the like and the granuleis molded by putting it in a die and pressurizing it to be like a plateand the like and obtain a raw formed body (green).

[0223] The raw formed body may be produced by layering green sheetsformed by a doctor blade method and the like.

[0224] Next, if necessary, parts to be through holes 135 into whichinsert lifter pins 136 are inserted to transport an object to be heatedsuch as a silicon wafer 139 and parts to be bottomed holes in whichtemperature measurement elements such as thermocouples are buried areformed.

[0225] Next, the raw formed body is heated and fired to be sintered soas to produce a plate-like body of a ceramic. After that, a ceramicsubstrate 111 is manufactured by processing the plate-like body into agiven shape (reference to FIG. 16(a)), however the plate-like body maypreviously be formed into a shape so as to use the plate-like body as itis. Also, the formed body is heated and fired while it is pressurizedfrom upper and lower sides to make it possible to manufacture apore-free ceramic substrate 111. Heating and firing may be carried outat a sintering temperature or more and in the case of a nitride ceramic,it is 1000 to 2500° C.

[0226] Incidentally, in general, the through holes 135 and the bottomedholes (not illustrated) to insert the temperature measurement elementsare formed after firing. The through holes 135 and the like can beformed by blast treatment such as a sand blast using SiC particle aftersurface grinding.

[0227] (2) Step of Printing Conductor Containing Paste to CeramicSubstrate

[0228] A conductor containing paste is generally a fluid with a highviscosity containing a metal particle, resin and a solvent. Theviscosity of the conductor containing paste is preferably 70 to 90 Pa·s.Since if the viscosity of the conductor containing paste is less than 70Pa·s, the viscosity is too low to produce a paste containing a metalwith an even concentration and it becomes difficult to form a conductorlayer with an even thickness, whereas if it exceeds 90 Pa·s, theviscosity of the paste is too high to do the application work easily andalso it becomes impossible to form a conductor layer with an eventhickness. In order to form a conductor layer having a roughened face,the viscosity of the conductor containing paste is preferable to behigh. Since the metal with a scaly or acicular shape is easy to becomeperpendicular or slantingly to the formation face of the resistanceheating element.

[0229] The conductor containing paste layer 112 m is formed by screenprinting by printing the conductor containing paste in a strip shaped ora ring shaped to the entire area where the resistance heating element isto be formed (FIG. 16(b)).

[0230] Since the resistance heating element patterns are required toheat the whole body of the ceramic substrate at an even temperature, thepatterns are preferable to be composed of arcs or concentric circleswhich are formed repeatedly as to draw some portions of concentriccircles as shown in FIGS. 1-3.

[0231] Incidentally, other than the above-mentioned method, theconductor layer can be formed by plating and in this case, by carryingout the plating so as to form an acicular plating layer, the resistanceheating element with a roughened surface can be formed. In such a case,it is preferable to form the acicular plating layer by forming a thinfilm by an electroless plating and the like and then carrying outelectroplating on the thin film.

[0232] Further, after a thick film plating layer is formed, etching iscarried out to form the roughened surface.

[0233] (3) Conductor Containing Paste Firing Step

[0234] The conductor containing paste layer printed at the bottom faceof the ceramic substrate 111 is heated and fired to remove the resin andthe solvent and at the same time to sinter the metal particle and bakethe particle in the bottom face of the ceramic substrate 111 to form theconductor layer with a given width (reference to FIG. 14) and afterthat, trimming treatment by laser as described above is performed toform resistance heating element (reference to FIG. 16).

[0235] In this case, the surface roughness of the conductor layersurface can be adjusted by changing the heating and firing conditions.The temperature of heating and firing is preferably 500 to 1000° C. andby firing at a relatively low temperature, the metal is prevented frommelting to be flattened and the surface roughness Ra of the conductorlayer can be adjusted to be 0.01 μm or more. Nevertheless, if thetemperature is too low, sintering of metal particles is not promoted andthe resistance value of the resistance heating element becomes too high,so that depending on the metal to be used, a proper firing temperaturehas to be selected.

[0236] After the conductor containing paste layer of the resistanceheating element patterns is formed by the above-mentioned screenprinting, plating, and sputtering methods, the layer is fired to be theresistance heating element 112 and the resistance value of theresistance heating element can be adjusted by laser trimming.

[0237] (4) Metal Covering Layer Formation

[0238] As shown in FIG. 14, a metal covering layer 1120 is preferable tobe formed on the surface of the resistance heating elements 112. Themetal covering layer 1120 may be formed by electroplating, electrolessplating, sputtering and the like and in consideration of massproductivity, the electroless plating is the most optimum.

[0239] (5) Attachment of Terminals and the Like

[0240] Terminals (external terminals 133) for connection to an electricpower source are attached to the terminal parts of the patterns of theresistance heating element 112 by a solder (FIG. 16(d)). Further,thermocouples are embedded in the bottomed holes 134 (not illustrated)and sealed with heat resistant resin of such as polyimide to complete aceramic heater.

[0241] Incidentally, the ceramic heater manufactured by themanufacturing methods of the second and the third aspect of the presentinventions can be used as an electrostatic chuck by formingelectrostatic electrodes in the inside of the ceramic substrate and alsocan be used as a wafer prober by forming a chuck top conductor layer onthe surface and guard electrodes and ground electrodes in the inside.

[0242] Next, a ceramic heater of the fourth aspect of the presentinvention will be described.

[0243] The ceramic heater of the fourth aspect of the present inventionis a ceramic heater comprising:

[0244] a ceramic substrate; and

[0245] a resistance heating element formed on a surface of said ceramicsubstrate,

[0246] wherein a gutter or a cut is formed at a part of said resistanceheating element.

[0247] In the ceramic heater of the fourth aspect of the presentinvention, as gutters or cuts formed in the part of the resistanceheating element, for example, similar ones to those described in themanufacturing methods of the ceramic heater of the second aspect of thepresent invention can be listed.

[0248] Also in the ceramic heater of the fourth aspect of the presentinvention, the surface roughness Ra of the surface of theabove-mentioned resistance heating element according to JIS B 0601 is0.01 μm or more and its preferable range is as described above.

[0249] Also, in the ceramic heater of the fourth aspect of the presentinvention, the above-mentioned resistance heating element is preferableto be covered with an insulating layer and, as the above-mentionedinsulating layer similar ones to the insulating covering of the ceramicheater of the first aspect of the present invention can be listed.

BEST MODE FOR CARRYING OUT THE INVENTION EXAMPLE 1

[0250] After a slurry was produced by mixing and kneading 100 parts byweight of an aluminum nitride powder (the average particle diameter of1.1 μm), 4 parts by weight of yttrium oxide (the average particlediameter of 0.4 μm), 12 parts by weight of an acrylic resin binder andalcohol, the slurry was sprayed by a spray drying method to produce agranular powder.

[0251] Next, the granular powder was put in a die and molded into a flatshape to obtain a raw formed body. The raw formed body was hot pressedat a temperature of 1800° C. and a pressure of 200 kg/cm² to obtain aplate-like sintered body of aluminum nitride with a thickness of 3 mm.Next, the sintered body was cut to obtain a ceramic substrate 11(reference to FIG. 11) for a ceramic heater.

[0252] Next, the ceramic substrate was bored by drilling-processing toform through holes 15 to insert lifter pins 16 for a semiconductor waferinto and bottomed holes 14 to embed thermocouples therein.

[0253] On the ceramic substrate 11 for which the above-mentionedprocessing was finished, for example, a conductor containing paste wasprinted by a screen printing method so as to form patterned strip-shapedresistance heating element 12 as shown in FIG. 1. The conductorcontaining paste employed in this case was Solvest PS 603D (trade name)manufactured by Tokuriki Chemical Research Co., Ltd., which was aso-called silver paste containing 7.5% by weight of metal oxidesconsisting of lead oxide, zinc oxide, silica, boron oxide, and alumina(5/55/10/25/10 by weight ratio in this order) in relation to the silver.The silver particle had an average particle diameter of 4.5 μm andmainly had a scaly shape.

[0254] The ceramic substrate 11 bearing the conductor containing pastewas heated and fired at 780° C. to sinter silver in the conductorcontaining paste and at the same time bake silver in the ceramicsubstrate. In this case, the resistance heating element 12 of the silversintered body had a thickness of about 10 μm, a width of about 2.4 mm,and the area resistivity of 5 mΩ/

.

[0255] After that, an insulating covering 17 of an oxide type glassmaterial was formed on the surface of the resistance heating element 12.

[0256] At first, a paste-like mixture was produced by mixing 87 parts byweight of glass powder having a composition comprising PbO: 30% byweight, SiO₂: 50% by weight, B₂O₃: 15% by weight, Al₂O₃: 3% by weight,and Cr₂O₃: 2% by weight with 3 parts by weight of a vehicle and 10 partsby weight of a solvent.

[0257] Next, using the paste-like mixture, screen printing was carriedout so as to cover the surface of the resistance heating element 12 toform a layer of the paste-like mixture. After that, the paste-likemixture was dried and fixed at 120° C. and fired at 680° C. for 10minutes in air to form an insulating covering 17 by being melted andadhered to the surface of the resistance heating element 12 and theceramic substrate 11. After that, the surface of the insulating coveringwas subjected to sand blast treatment using a SiC powder with an averageparticle diameter of 10 μm to adjust the surface roughness Ra of theinsulating covering. At that time, the thickness of the insulatingcovering 17 was 10 μm. However, the insulating covering 17 was notformed in the connecting portions of the external terminals 133 in bothends of circuits comprising the resistance heating element 12.Accordingly, the covering state in the vicinity of the externalterminals was different from the ceramic heater 10 shown in FIG. 2.

[0258] Incidentally, at the time of fusion bonding by heating, a methodinvolving preliminary molding in a shape to be fitted with the shape ofthe insulating covering 17 and then putting the preliminarily formedbody on the resistance heating element 12 and heating the formed body,may be employed as well.

[0259] Next, a silver-containing lead paste (made by Tanaka KikinzokuKogyo K. K.) was printed in the parts of the resistance heating element12 where the external terminals 13 were to be formed to form a solderlayer and further, external terminals 13 made of Kovar were put on thesolder layer and heated at 420° C. to carry out reflow and the externalterminals 13 were attached to and fixed in the both end parts of theresistance heating element 12.

[0260] Incidentally, as shown in FIG. 2, the resistance heating element12 and the external terminals 13 were connected and after that, theinsulating covering 17 might be formed so as to cover the parts of theresistance heating element 12 where the external terminals 13 wereformed.

[0261] After that, thermocouples (not illustrated) for controlling thetemperature of the substrate were inserted into the bottomed holes 14 ofthe ceramic substrate to obtain a ceramic heater 10 as shown in FIG. 1and FIG. 2 and the ceramic heater 10 was fitted in a supporting in whicha heat insulating ring made of fluoro resin for fitting the ceramicheater was formed in the upper part to obtain a hot plat unit.

[0262] Incidentally, since the resistance heating element had a givenresistance value, when electric power was applied, heat was generateddue to the Joule's heat to heat a semiconductor wafer 19.

[0263] Regarding the ceramic heater 10 constituting the hot plate unit,the thermal expansion coefficient of the insulating covering wasmeasured and evaluation was carried out by the following methods.

[0264] Evaluation Methods

[0265] (1) Measurement of Surface Roughness Ra of Insulating Covering

[0266] Using Therfcom 920A manufactured by Tokyo Seimitsu Co., Ltd., thesurface roughness Ra and Rmax were measured.

[0267] (2) Measurement of Surface Resistance (Area Resistivity) ofInsulating Covering Material

[0268] Measurement was carried out at a room temperature and D.C. 100 V.

[0269] (3) Evaluation of Oxidation Resistance of Resistance HeatingElement

[0270] Evaluation was carried out by investigating the change of theheater resistance after aging in 200° C.×1000 hours.

[0271] (4) Evaluation of Dispersion of Temperature Rising Time

[0272] After a silicon wafer was put on the hot plate unit, the time(temperature rising time) taken to heat the silicon wafer to 200° C. wasmeasured 10 times and the ratio of the quickest temperature rising timeor the slowest temperature rising time in relation to the averagetemperature rising time was calculated by % and the higher absolutevalue calculated by subtraction from 100% was set to be the dispersionof the temperature rise.

[0273] (5) Temperature Dropping Time

[0274] After the temperature rise was carried out in the conditions ofthe above-mentioned (4), a coolant at 25° C. (cooling air) was suppliedat 0.1 m³/minute and the time (temperature dropping time) taken forcooling to 50° C. was measured and the average value was set to be thetemperature dropping time.

[0275] (6) Sulfurization Resistance

[0276] The ambient atmosphere containing 15% by volume of H₂S was keptat 75° C. and the ceramic heater was left for 10 days in the ambientatmosphere and the resistance alteration ratio of the resistance heatingelement was measured for the evaluation of the result as thesulfurization resistance.

[0277] (7) Occurrence of Migration

[0278] The hot plate unit was heated to 200° C. in 100% humidity,electric power was applied for 48 hours and the occurrence of metaldiffusion among resistance heating element patterns was measured by afluorescent x-ray analyzer (EPM-810S manufactured by ShimadzuCorporation).

EXAMPLE 2

[0279] A ceramic heater was manufactured in the same manner as Example 1and subjected to the evaluation similarly to Example 1, except that inplace of the oxide type glass material, a heat resistant resin material(polyimide resin) was used and the insulating covering 17 was formed andthe roughening treatment was carried out by the following method. Theresults were shown in Table 1.

[0280] That is, at first after a solution of a mixture in a paste-likeor viscous liquid-like state containing 80% by weight of an aromaticpolyimide powder and 20% by weight of polyamide acid was produced, thesolution of the mixture was selectively applied so as to cover thesurface of the resistance heating element 12 and form a layer of themixture on the surface of the resistance heating element 12.

[0281] Next, the formed layer of the mixture was heated at 350° C. anddried and solidified in a continuously firing furnace to carry out meltbonding of the mixture to the surface of the resistance heating element12 and the ceramic substrate 11. After that, the surface of theinsulating covering was subjected to sand blast treatment using analumina powder with an average particle diameter of 1.0 μm to adjust thesurface roughness Ra of the insulating covering 17. In this case, theaverage thickness of the formed insulating covering 17 was 10 μm.

EXAMPLE 3

[0282] A ceramic heater was manufactured in the same manner as Example 1and subjected to the evaluation similarly to Example 1, except that inplace of the oxide type glass material, a heat resistant resin material(silicone type resin) was used and the insulating covering 17 was formedand the roughening treatment was carried out by the following method.The results were shown in Table 1.

[0283] That is, methylphenyl type silicone resin was selectively appliedso as to cover the surface of the resistance heating element 12 by ametal mask printing method and the like and heated at 220° C. and driedand solidified in an oven to carry out melt bonding of the resin to thesurface of the resistance heating element 12 and the ceramic substrate11. At that time, the thickness of the formed insulating covering 17 was15 μm. The surface roughness Ra of the insulating covering 17 wasadjusted by sand blast treatment using an alumina powder with an averageparticle diameter of 1.5 μm.

EXAMPLE 4

[0284] In this example, a ceramic heater was manufactured in the samemanner as Example 1 and subjected to the evaluation similarly to Example1, except that the resistance value of the strip-shaped resistanceheating element was increased and the thickness of the insulatingcovering comprising oxide glass was adjusted to be 20 μm. The resultswere shown in Table 1.

[0285] That was because the resistance value was required to be high inthe case of applying voltage of 30 to 300 V to raise the temperature to200° C. or more. Incidentally, the adjustment of the surface roughnessRa of the insulating covering 17 was conducted by sand blast treatmentusing an SiC powder with an average particle diameter of 0.1 μm.

[0286] As the paste for the resistance heating element, a pastecontaining silver: 56.6% by weight, palladium: 10.3% by weight, SiO₂:1.1% by weight, B₂O₃: 2.5% by weight, ZnO: 5.6% by weight, PbO: 0.6% byweight, RuO₂: 2.1% by weight, a resin binder 3.4% by weight, and asolvent: 17.9% by weight was used.

[0287] The resistance heating element patterns had a thickness of 10 μm,a width of 2.4 mm, and an area resistivity of 150 mΩ/

.

EXAMPLE 5

[0288] A ceramic heater was manufactured in the same manner as Example 4and subjected to the evaluation similarly to Example 4, except that inplace of the oxide type glass material, a heat resistant resin material(polyimide resin) was used and the insulating covering 17 was formed andthe roughening treatment was carried out by the method as described inExample 2. The thickness of the insulating covering was adjusted to 10μm and the surface roughness Ra of the insulating covering 17 wasadjusted by sand blast treatment using an alumina powder with an averageparticle diameter of 0.1 μm. The results were shown in Table 1.

EXAMPLE 6

[0289] A ceramic heater was manufactured in the same manner as Example 4and subjected to the evaluation similarly to Example 4, except that inplace of the oxide type glass material, a heat resistant resin material(silicone type resin) was used and the insulating covering 17 was formedand the roughening treatment was carried out by the method as describedin Example 3. The thickness of the insulating covering was adjusted to10 μm and the surface roughness Ra of the insulating covering 17 wasadjusted by sand blast treatment using an alumina powder with an averageparticle diameter of 0.03 μm. The results were shown in Table 1.

COMPARATIVE EXAMPLE 1

[0290] A ceramic heater was manufactured in the same manner as Example 1and subjected to the evaluation similarly to Example 1, except that theceramic substrate bearing the resistance heating element thereon wasimmersed in an electroless nickel plating bath to form a metal layer ofnickel with a thickness of about 1 μm on the surface of the resistanceheating element. The results were shown in Table 1.

[0291] The concentrations of the respective components of theabove-mentioned nickel plating bath were nickel sulfate 80 g/l, sodiumhypophosphite 24 g/l, sodium acetate 12 g/l, boric acid 8 g/l, andammonium chloride 6 g/l.

COMPARATIVE EXAMPLE 2

[0292] A ceramic heater was manufactured in the same manner as Example 1and subjected to the evaluation similarly to Example 1, except that nosurface roughening treatment was carried out after the insulatingcovering was formed on the surface of the resistance heating element 12.Incidentally, the surface roughness Ra of the ceramic heater was 0.07μm. The results were shown in Table 1.

COMPARATIVE EXAMPLE 3

[0293] A ceramic heater was manufactured in the same manner as Example 4and subjected to the evaluation similarly to Example 1, except that sandblast treatment using a SiC powder with an average particle diameter of15 μm was carried out after the insulating covering was formed on thesurface of the resistance heating element 12 to form an insulatingcovering with a surface roughness Ra of 11 μm. The results were shown inTable 1.

COMPARATIVE EXAMPLE 4

[0294] A ceramic heater was manufactured in the same manner as Example 1and subjected to the evaluation similarly to Example 1, except that noinsulating covering was formed on the surface of the resistance heatingelement 12. The results were shown in Table 1. TABLE 1 Surface Thermalroughness Ra expansion Area Oxidation Dispersion of coefficientresistivity resistance of Temperature insulating of of (resistivitytemperature dropping Sulfur- covering insulating insulating change inrising time time (from ization Insulating covering Ra (μm) coveringcovering 200° C. × 1000 Hr) (from 25 to 200 to 150° C. resis- TypeComposition Rmax (μm) (ppm/° C.) (Ω/□) (%) 200° C.) (%) (second) tance(%) Example 1 Oxide glass PbO—SiO₂— Ra = 0.861 5 10¹⁶ 0.2 0.1 110 0 B₂O₃Rmax = 11.3 Example 2 Polyimide Aromatic type Ra = 0.868 12 10¹⁵ 0.3 0.2120 0 resin Rmax = 6.775 Example 3 Silicone type Methylphenyl Ra = 1.00913 10¹⁵ 0.3 0.1 130 0 resin type Rmax = 6.74 Example 4 Oxide glassPbO—SiO₂— Ra = 0.097 5 10¹⁶ 0.1 0.1 110 0 B₂O₃ Rmax = 1.00 Example 5Polyimide Aromatic Ra = 0.086 12 10¹⁵ 0.3 0.2 130 0 resin type Rmax =1.02 Example 6 Silicone Methylphenyl Ra = 0.022 13 10¹⁵ 0.3 0.4 120 0type resin type Rmax = 1.23 Comparative Plate Nickel — 13.3 50 m 3 0.190 0 Example 1 Comparative Oxide glass PbO—SiO₂— Ra = 0.007 5 10¹⁶ 0.20.5 160 0 Example 2 B₂O₃ Comparative Oxide glass PbO—SiO₂— Ra = 11 510¹⁶ 0.2 0.5 180 0 Example 3 B₂O₃ Comparative — — — — — 20 0.5 90 200Example 4

[0295] As being made clear from the results shown in Table 1, inExamples 1 to 6, the resistance change of the resistance heating elementwas as small as 0.1 to 0.3%, whereas in Comparative Example 1, it washigh, that is 3%. The reason for that was attributed to resistancealteration owing to the oxidation of the nickel plating film itself andother than that, it was supposed that the nickel plating film wasporous, thus diffusion of oxygen and oxidization of the silver occurs inthe inside. Further, in Examples 1 to 6, the dispersion of thetemperature rising time was small and the temperature dropping speed wasrelatively quick, whereas in Comparative Examples 2, 3, since thesurface roughness Ra of the insulating covering covering the resistanceheating element was too low or too high, the temperature dropping speedwas retarded.

[0296] Further, regarding the occurrence of migration, in the ceramicheater according to Comparative Example 4, Ag migration took place andoccurrence of short-circuit among the resistance heating elementpatterns was highly probable.

[0297]FIG. 6 to FIG. 10 respectively show the graphs showing themeasurement results of the surface roughness of the insulating coveringsconstituting the ceramic heaters according to Examples 1 to 5.

[0298] Further, in the ceramic heaters according to Examples 1 and 4,the thermal expansion coefficient of the oxide glass, the insulatingcovering, was 5 ppm/° C. and it was approximately numerically similar tothat of aluminum nitride, 3.5 to 4 ppm/° C. and consequently, theresistance change caused by separation of metal particles constitutingthe resistance heating element owing to expansion and contraction causedin cooling and heating cycles was relatively small as compared with thatin the case of using the heat resistant resin.

[0299] In Examples 4 to 6, as the resistance heating element, thosehaving an area resistivity of 150 mΩ/

were used. In this case, since the area resistivity of the insulatingcovering was 10¹⁵ to 10¹⁶ Ω/

, which is almost complete insulator, even if voltage of 50 to 200 V wasapplied, the electric current was transmitted in the inside of theresistance heating element and the calorific value was also increased,whereas in the case of forming a nickel plating film as ComparativeExample 1, the area resistivity of the nickel plating film was 50 mΩ/

, smaller than that of the resistance heating element, and sinceelectric current is transmitted in parts having a lower resistancevalue, electric current was transmitted through the nickel plating filmto result in low calorific value.

EXAMPLE 7

[0300] A ceramic substrate 21 for a ceramic heater was manufactured inthe same manner as Example 1 and parts to be through holes 25 to insertlifter pins 16 for a semiconductor wafer into and to be bottomed holes24 to embed thermocouples therein were bored by drilling process.

[0301] Next, in the bottom face of the ceramic substrate 21 for whichthe above-mentioned processing was finished, the resistance heatingelement patterns 22 a to 22 f with a shape shown in FIG. 3 were formedusing the same material as Example 1.

[0302] After that, as shown in FIG. 3, at the resistance heating elementpatterns 22 a, 22 b, and 22 c, the insulating coverings 27 a, 27 b, and27 c of an oxide glass material were formed to cover the areassandwiched by resistance heating element constituting circuits and thestretch of the periphery thereof. And on the other hand, at theresistance heating element patterns 22 d, 22 e, and 22 f, the insulatingcovering 27 d comprising the same material is formed to cover the areassandwiched by resistance heating element patterns constituting circuitsand their peripheral area and entire area among the respective circuits.

[0303] The composition of the above-mentioned oxide glass material wasthe same as in the case of Example 1, the formation method of theinsulating covering 27 was same as that of Example 1 except that thecovering areas were extended in a wide area as described above. In thiscase, the thickness of the insulating covering 27 was 30 μm. However,the portions of both ends of the circuits to be connected with externalterminals were not covered with the insulating covering 27. The surfaceroughness Ra of the insulating covering 27 was adjusted by sand blasttreatment using a SiC powder with an average particle diameter of 5 μm.

[0304] After that, thermocouples (not illustrated) for temperaturecontrol were embedded in the bottomed holes 24 of the ceramic substrateto obtain the ceramic heater 20 shown in FIG. 3 and FIG. 4.

[0305] As described above, after the ceramic heater 20 was manufacturedusing the aluminum nitride substrate 21, evaluation was carried outsimilarly to Example 1. The results were shown in Table 2.

EXAMPLE 8

[0306] A ceramic heater was manufactured in the same manner as Example 7and subjected to the evaluation similarly to Example 7, except that inplace of the oxide type glass material, a heat resistant resin material(polyimide resin) was used and the insulating covering 27 was formed andthe roughening treatment was carried out by the following method. Theresults were shown in Table 2.

[0307] That is, at first after a solution of a mixture in a paste-likeor viscous liquid-like state containing 80% by weight of an aromaticpolyimide powder and 20% by weight of polyamide acid was produced, thesolution of the mixture was selectively applied so as to cover thesimilar areas to those of Example 7 and heated at 350° C. and dried andsolidified in a continuously firing furnace to form the insulatingcoverings 27 a to 27 d. The thickness of the insulating covering 27 was30 μm and the surface roughness Ra of the insulating covering 27 wasadjusted by sand blast treatment using an alumina powder with an averageparticle diameter of 4.2 μm.

EXAMPLE 9

[0308] A ceramic heater was manufactured in the same manner as Example 7and subjected to the evaluation similarly to Example 7, except that inplace of the oxide type glass material, a heat resistant resin material(silicone type resin) was used and the insulating covering 27 was formedand the roughening treatment was carried out by the following method.The results were shown in Table 2.

[0309] That is, methylphenyl type silicone resin was selectively appliedso as to cover the surface of the resistance heating element 12 by ametal mask printing method and the like and heated at 220° C. and driedand solidified to form the insulating coverings 27 a to 27 d. Thethickness of the insulating covering 27 was 30 μm. The surface roughnessRa of the insulating covering 27 was adjusted by sand blast treatmentusing an alumina powder with an average particle diameter of 2.0 μm.TABLE 2 Surface Thermal roughness Ra expansion Sheet OxidationDispersion of coefficient resistivity resistance of Temperatureinsulating of of (resistivity temperature dropping Sulfur- coveringinsulating insulating change in rising time time (from izationInsulating covering Ra (μm) covering covering 200° C. × 1000 Hr) (from25 to 200 to 150° C. resis- Type Composition Rmax (μm) (ppm/° C.) (Ω/□)(%) 200° C.) (%) (second) tance (%) Example 7 Oxide PbO—SiO₂— Ra = 4.0305 10¹⁶ 0.2 0.1 110 0 glass B₂O₃ Rmax = 20.52 Example 8 PolyimideAromatic type Ra = 3.250 12 10¹⁵ 0.3 0.1 120 0 resin Rmax = 20.92Example 9 Silicone Methylphenyl Ra = 2.040 13 10¹⁵ 0.3 0.1 130 0 typetype Rmax = 15.30 resin

[0310] As being made clear from the results shown in Table 2, also inExamples 7 to 9, the area resistivity of the insulating coverings was ashigh as 10¹⁵ to 10¹⁶ Ω/

and the resistance change of the resistance heating element covered withsuch insulating coverings was as small as 0.2 to 0.3%. Further, thedispersion of the temperature rising time was small and the temperaturedropping speed was relatively quick.

[0311] Further, after the oxidation resistant test was carried out inExamples 8, 9, the insulating covering 27 was forcibly peeled off fromthe surface of the ceramic substrate and observation for checkingwhether migration of a metal such as silver on the surface of theresistance heating element took place or not, was carried out in thesame manner as Example 1. As a result, no migration was found takingplace.

EXAMPLE 10

[0312] A composition containing 100 parts by weight of a SiC powder(average particle diameter: 1.1 μm), 4 parts by weight of B₄C, 12 partsby weight of an acrylic binder, and alcohol was spray dried to produce agranular powder.

[0313] Next, the granular powder was put in a die and molded into a flatshape to obtain a raw formed body and the raw formed body was hotpressed at a temperature of 1890° C. and a pressure of 20 MPa to obtaina plate-like sintered body of SiC with a thickness of about 3 mm. Next,the surface of the plate-like sintered body was ground by diamond wheelof #800 and grinded with a diamond paste to adjust to: Ra=0.008 μm.Further, a glass paste (G-5177 made by Shouei Chemical Products Inc.)was applied and heated to 600° C. to form a SiO₂ layer with a thicknessof 3 μm.

[0314] Then, the plate-like sintered body was cut to obtain a disk-likebody with a diameter of 210 mm as a ceramic substrate. After that, theface where the above-mentioned SiO₂ layer was formed was used for theface where the resistance heating element was to be formed and as shownin FIG. 5, a ceramic heater was produced in the same manner as Example1, except that the insulating covering (oxide glass) with a thickness of50 μm was formed in the entire areas where the resistance heatingelement was formed and roughened surface was formed by sand blasttreatment using a SiC powder with an average particle diameter of 10 μm.

[0315] As described above, after the ceramic heater was produced usingthe substrate of SiC, evaluation was carried out similarly to Example 1.The results were shown in Table 3.

EXAMPLE 11

[0316] A ceramic heater was manufactured in the same manner as Example10 and subjected to the evaluation similarly to Example 10, except thatin place of the oxide type glass material, a heat resistant resinmaterial (polyimide resin) was used and the insulating covering 37 wasformed and the roughening treatment was carried out by sand blast usingan alumina powder with an average particle diameter of 10 μm. Theresults were shown in Table 3.

[0317] That is, at first after a solution of a mixture in a paste-likeor viscous liquid-like state containing 80% by weight of an aromaticpolyimide powder and 20% by weight of polyamide acid was produced, thesolution of the mixture was applied so as to cover the entire areaswhere the resistance heating element 12 was formed and form a layer ofthe mixture.

[0318] After that, the formed layer of the mixture was heated at 350° C.and dried and solidified in a continuously firing furnace to melt themixture and let it adhered to the surface of the resistance heatingelement and the ceramic substrate, and then roughening treatment wascarried out in the above-mentioned conditions. In this case, thethickness of the formed insulating covering was 50 μm.

EXAMPLE 12

[0319] A ceramic heater was manufactured in the same manner as Example10 and subjected to the evaluation similarly to Example 10, except thatroughening treatment using a SiC powder with an average particlediameter of 8 μm was carried out for the insulating covering (oxideglass). The results were shown in Table 3.

EXAMPLE 13

[0320] A ceramic heater was manufactured in the same manner as Example10 and subjected to the evaluation similarly to Example 10, except thatin place of the oxide type glass material, a heat resistant resinmaterial (polyimide resin) was used and the insulating covering 37 wasformed similarly to Example 11 and roughening treatment using an aluminapowder with an average particle diameter of 8 μm was carried out. Theresults were shown in Table 3. TABLE 3 Surface Thermal roughness Raexpansion Area Oxidation Dispersion of coefficient resistivityresistance of Temperature insulating of of (resistivity temperaturedropping Sulfur- covering insulating insulating change in rising timetime (from ization Insulating covering Ra (μm) covering covering 200° C.× 1000 Hr) (from 25 to 200 to 150° C. resis- Type Composition Rmax (μm)(ppm/° C.) (Ω/□) (%) 200° C.) (%) (second) tance (%) Example OxidePbO—SiO₂— Ra = 8.230 5 10¹⁶ 0.2 0.4 110 0 10 glass B₂O₃ Rmax = 100.01Example Polyimide Aromatic type Ra = 9.352 12 10¹⁵ 0.3 0.5 120 0 11resin Rmax = 150.32 Example Oxide PbO—SiO₂— Ra = 7.252 5 10¹⁶ 0.2 0.4130 0 13 glass B₂O₃ Rmax = 98.32 Example Polyimide Aromatic type Ra =6.252 12 10¹⁵ 0.3 0.4 120 0 12 resin Rmax = 82.32

[0321] As being made clear from the results shown in Table 3, inExamples 10 to 13, the resistance change of the resistance heatingelement was as small as 0.2 to 0.3%. Further, the dispersion of thetemperature rising time was slightly high as compared with those ofExamples 1 to 7, attributed to high surface roughness of the insulatingcovering, however the temperature dropping speed was not so much changedand relatively quick.

[0322] As described above, the ceramic heater of the first aspect of thepresent invention had a small resistance change ratio, slight dispersionof temperature rising time, a high temperature dropping time, and wasexcellent in temperature controllability. Further, it was excellent inthe corrosion resistance to reactive gas such as O₂ and H₂S in asemiconductor producing device.

[0323] Further, since the insulating covering was of an insulator, evenif the resistance value of the resistance heating element was increased,no electric current flowed in the insulating covering and a heaterhaving a usable range of 150° C. or more was able to be obtained.

[0324] Also, in the case the oxide glass was used for the insulatingcovering, since it had excellent adhesion property to the ceramicsubstrate and had a small thermal expansion coefficient, cracks werehardly formed and at the same time, the resistance change ratio of theresistance heating element was small.

[0325] Further, in the case the heat resistant resin was used for theinsulating covering, the insulating covering could be formed at arelatively low temperature.

[0326] As described above, the ceramic heater of the first aspect of thepresent invention was the most optimum to be used as a heater for amiddle temperature range from 200 to 400° C. and a high temperaturerange from 400 to 800° C.

EXAMPLE 14 Adjustment of Resistance Value of Resistance Heating Elementby Laser Trimming

[0327] (1) A composition containing 100 parts by weight of an aluminumnitride powder (average particle diameter: 0.6 μm), 4 parts by weight ofyttria (average particle diameter: 0.4 μm), 12 parts by weight of anacrylic resin binder, and alcohol was spray dried to produce a granularpowder.

[0328] (2) Next, the granular powder was put in a die and molded into aflat shape to obtain a raw formed body (a green).

[0329] (3) The raw formed body was hot pressed at a temperature of 1800°C. and a pressure of 20 MPa to obtain a plate-like aluminum nitride bodywith a thickness of 3 mm.

[0330] Next, the plate-like body was cut to obtain a disk-like body witha diameter of 210 mm and made to be a plate-like body comprising aceramic (a ceramic substrate 111). The ceramic substrate was subjectedto drilling-process to form through holes 135 to insert lifter pins fora silicon wafer into and bottomed holes 134 (the diameter: 1.1 mm; thedepth: 2 mm) to embed thermocouples in.

[0331] (4) A conductor containing paste layer was formed on the ceramicsubstrate 111 obtained in the above-mentioned (3) by screen printing.The printed patterns were the patterns as shown in FIG. 3.

[0332] As the conductor containing paste, a paste having a compositioncontaining Ag: 48% by weight, Pt: 21% by weight, SiO₂: 1.0% by weight,B₂O₃: 1.2% by weight, ZnO: 4.1% by weight, PbO: 3.4% by weight, ethylacetate: 3.4% by weight, and butyl carbitol: 17.9% by weight wasemployed.

[0333] The conductor containing paste was Ag—Pt paste and silverparticle (Ag-540 made by Shouei Chemical Products Inc.) had an averageparticle diameter of 4.5 μm and a scaly shape. The Pt particle (Pd-221made by Shouei Chemical Products Inc.) had an average particle diameterof 6.8 μm and a spherical shape.

[0334] The viscosity of the conductor containing paste was 80 Pa·s.

[0335] (5) Further, after formation of the conductor containing pastelayer of the heating element patterns, the ceramic substrate 111 washeated and fired at 850° C. for 10 to 20 minutes to sinter Ag and Pt inthe conductor containing paste and at the same time bake them on theceramic substrate.

[0336] The resistance heating element patterns had as shown in FIG. 13,seven channels 112 a to 112 g. The dispersion of the resistance valuesof the four channels (the resistance heating element patterns 112 a to112 d) in the periphery before performing trimming was 7.4 to 12.4%.

[0337] Incidentally, the term, channel, means a circuit to be controlledsolely by applying same voltage and in this example, denotes therespective resistance heating element patterns (112 a to 112 g) formedas continuous bodies.

[0338] The resistance dispersion in the respective channels (theresistance heating element patterns 112 a to 112 d) was calculated asfollows. That is, at first, each channel was divided into twentydivisions and resistance thereof was measured between both ends in thedivisions. Then, the average value thereof was defined as the averagedivision resistance and then, the dispersion was calculated from thedifference between the highest resistance value and the lowestresistance value and the average division resistance value. Further, theresistance value in the respective channels (the resistance heatingelement patterns 112 a to 112 d) is the total of the resistance valuesmeasured separately.

[0339] (6) Next, using YAG laser (S143AL, manufactured by NEC, output 5W, pulse frequency set range 0.1 to 40 kHz) having wavelength of 1060 nmas an equipment for trimming, the pulse frequency was set to be 1.0 kHz.The equipment was equipped with an X-Y stage, a galvanomirror, a CCDcamera, Nd: YAG laser and a controller built therein to control thestage and the galvanomirror, and the controller was connected to acomputer (FC-9821, manufactured by NEC). The computer was provided witha CPU working as a computing unit and a memory unit and also providedwith a hard disk and a 3.5-inch FD drive working as a memory unit and aninput unit.

[0340] The resistance heating element pattern data was inputted from theFD drive to the computer and the position of the resistance heatingelement was read out (reading was carried out on the bases of markersformed in specified points of the conductor layer or in the ceramicsubstrate). Then, necessary control data was computed and the resistanceheating element patterns were irradiated in the direction approximatelyparallel along the direction of electric current flow to remove theconductor layer in the irradiated portions and form gutters with a widthof 50 μm reaching the ceramic substrate, so that the resistance valuewas adjusted. The resistance heating element had a thickness of 5 μm anda width of 2.4 mm. The laser was irradiated with a frequency of 1 kHz,an output of 0.4 W, a bit size of 10 μm, and a processing speed of 10mm/second.

[0341] In such a manner, trimming was performed and the dispersion ofthe resistance values of four channels (resistance heating elementpatterns 112 a to 112 d) in the periphery after the adjustment of theresistance value of the resistance heating element was remarkablydecreased to 1.0 to 5.0%.

[0342] (7) Next, Ni plating was carried out for the portions to whichthe external terminals 133 were to be attached in order to assure theconnection to an electric power, a silver-lead solder paste (made byTanaka Kikinzoku Kogyo K. K.) was printed to form solder layers byscreen printing.

[0343] Then, external terminals 133 made of Kovar were put on the solderlayers and heated at 420° C. to carry out reflow and the externalterminals 133 were attached to the surface of the resistance heatingelement patterns.

[0344] (8) Thermocouples for controlling the temperature were sealedwith polyimide to obtain a ceramic heater 110.

EXAMPLE 15 Production of Ceramic Heater (Resistance Heating ElementFormation by Laser Trimming)

[0345] In this example, a ceramic heater having the resistance heatingelement patterns shown in FIG. 13 was manufactured.

[0346] (1) A composition containing 100 parts by weight of an aluminumnitride powder (average particle diameter: 1.1 μm), 4 parts by weight ofyttria (average particle diameter: 0.4 μm) 12 parts by weight of anacrylic resin binder, and alcohol was spray dried to produce a granularpowder.

[0347] (2) Next, the granular powder was put in a die and molded into aflat shape to obtain a raw formed body (a green).

[0348] (3) The raw formed body was hot pressed at a temperature of 1800°C. and a pressure of 20 MPa to obtain a plate-like aluminum nitride bodywith a thickness of some 3 mm.

[0349] Next, the plate-like body was cut to obtain a disk with adiameter of 210 mm and made to be a plate-like body made of a ceramic (aceramic substrate 111). The ceramic substrate was subjected todrilling-process to form through holes 135 to insert lifter pins 136 fora silicon wafer into and bottomed holes (not illustrated) (the diameter:1.1 mm; the depth: 2 mm) to embed thermocouples in (reference to FIG.16(a)).

[0350] (4) A conductor containing paste layer 112 m was formed on theceramic substrate 111 obtained in the above-mentioned (3) by screenprinting. The printed patterns were the concentric circles-like(ring-shaped) patterns having a given width and formed in a plane-shapeso as to include the resistance heating element patterns 112 a to 112 gwhich are going to be the respective circuits of the resistance heatingelement shown 112 in FIG. 13 (reference to FIG. 16(b)).

[0351] As the conductor containing paste, a silver paste containing 7.5parts by weight of metal oxides consisting of lead oxide: 5% by weight,zinc oxide: 55% by weight, silica: 10% by weight, boron oxide: 25% byweight, and alumina: 5% by weight in 100 parts by weight of silver wasemployed. The silver particle (Ag-540, made by Shouei Chemical ProductsInc.) had an average particle diameter of 4.5 μm and a scaly shape.

[0352] The viscosity of the conductor containing paste was 80 Pa·s.

[0353] (5) Further, after formation of the conductor containing pastelayer of the heating element patterns, the ceramic substrate 111 washeated and fired at 780° C. for 20 minutes to sinter silver in theconductor containing paste and at the same time bake them on the ceramicsubstrate.

[0354] (6) Next, using YAG laser (S143AL, manufactured by NEC, output 5W, pulse frequency set range 0.1 to 40 kHz) having wavelength of 1060 nmwas used as an equipment for trimming, the pulse frequency was set to be1.0 kHz to perform trimming.

[0355] The equipment was equipped with an X-Y stage, a galvanomirror, aCCD camera, Nd: YAG laser and a controller built therein to control thestage and the galvanomirror and the controller was connected to acomputer (FC-9821, manufactured by NEC). The computer was provided witha CPU working as a computing unit and a memory unit and also providedwith a hard disk and a 3.5-inch FD drive working as a memory unit and aninput unit.

[0356] The X-Y stage was made to be rotatable at optional angle θ aroundfixed center axis A of the ceramic substrate.

[0357] The resistance heating element pattern data was inputted from theFD drive to the computer and the position of the resistance heatingelement was read out (reading was carried out on the basis of markersformed in specified points of the conductor layer or in the ceramicsubstrate) and necessary control data was computed and while the ceramicsubstrate 111 being rotated, laser beam was irradiated to the portionsof the conductor containing paste layer other than the areas whereresistance heating element patterns were to be formed to remove theconductor containing paste layer in the irradiated portions and form theresistance heating element 112 with patterns shown in FIG. 13 (referenceto FIG. 16(c)). The resistance heating element had a thickness of 5 μm,a width of 2.4 mm, and an area resistivity of 7.7 mΩ/

.

[0358] (7) Next, the ceramic substrate 111 produced in theabove-mentioned (6) was immersed in an electroless nickel plating bathof an aqueous solution containing nickel sulfate 80 g/l, sodiumhypophosphite 24 g/l, sodium acetate 12 g/l, boric acid 8 g/l, andammonium chloride 6 g/l to form a metal covering layer (a nickel layer)1120 with a thickness of about 1 μm on the surface of the silver-leadresistance heating element 112.

[0359] (8) Solder layers were formed on the portions to which theexternal terminals 133 were to be attached in order to assure theconnection to an electric power by printing a silver-lead solder paste(made by Tanaka Kikinzoku Kogyo K.K.) by screen printing.

[0360] Then, external terminals 133 made of Kovar were put on the solderlayers and heated at 420° C. to carry out reflow and the externalterminals 133 were attached to the surface of the resistance heatingelement 112 (FIG. 16(d)).

[0361] (9) Thermocouples for controlling the temperature were sealedwith polyimide to obtain a ceramic heater 110.

EXAMPLE 16 Adjustment of Resistance Value of Resistance Heating Elementby Laser Trimming

[0362] A ceramic heater was manufactured in the same manner as Example14 except that in the step (5) of Example 14, surface roughening wascarried out by sand blast treatment using Al₂O₃ (the average particlediameter: 10 μm) after baking the Ag—Pt paste applied to the ceramicsubstrate.

EXAMPLE 17 Adjustment of Resistance Value of Resistance Heating Elementby Laser Trimming

[0363] A ceramic heater was manufactured in the same manner as Example14 except that in the step (5) of Example 14, surface roughening wascarried out by sand blast treatment using Al₂O₃ (the average particlediameter: 20 μm) after baking the Ag—Pt paste applied to the ceramicsubstrate.

EXAMPLE 18

[0364] A ceramic heater made of silicon carbide was manufactured in thesame manner as Example 14 except that silicon carbide with an averageparticle diameter of 1.0 μm was used in stead of aluminum nitride andthe sintering temperature was set at 1900° C. and further, after a glasspaste containing 50 parts by weight of a glass powder (borosilicateglass) with an average particle diameter of 0.5 μm, 20 parts by weightof ethyl alcohol, and 5 parts by weight of polyethylene glycol wasapplied to the surface of the obtained heater plate, an SiO₂ layer witha thickness of 10 μm was formed on the surface by firing it at 1500° C.for 2 hours and alumina (the average particle diameter: 0.01 μm) wasused for sand-blasting.

EXAMPLE 19

[0365] A ceramic heater made of silicon carbide was manufactured in thesame manner as Example 14 except that silicon carbide with an averageparticle diameter of 1.0 μm was used and the sintering temperature wasset at 1900° C. and further after a glass paste (borosilicate glass)containing 50 parts by weight of a glass powder with an average particlediameter of 0.5 μm, 20 parts by weight of ethyl alcohol, and 5 parts byweight of polyethylene glycol was applied to the surface of the obtainedheater plate, an SiO₂ layer with a thickness of 10 μm was formed on thesurface by firing it at 1500° C. for 2 hours and alumina (the averageparticle diameter: 0.01 μm) was used for the sand blasting.

COMPARATIVE EXAMPLE 5 Adjustment of Resistance Value of ResistanceHeating Element by Laser Trimming

[0366] A ceramic heater was manufactured in the same manner as Example14, except that the resistance heating element was formed by using aconductor containing paste having the following composition and heatingand firing the paste.

[0367] The conductor containing paste was a Ag—Pt paste with acomposition same as that in Example 14 and the silver particle (Ag-128,made by Shouei Chemical Products Co., Ltd.) had an average particlediameter of 0.6 μm and a spherical shape. The Pt particle (Pd-215, madeby Shouei Chemical Products Co., Ltd.) had an average particle diameterof 0.6 μm and a spherical shape.

[0368] The viscosity of the conductor containing paste was 80 Pa·s.

[0369] Further, after the conductor containing paste layer in theheating element patterns was formed, the ceramic substrate 111 washeated and fired at 850° C. for 20 minutes to sinter Ag and Pt in theconductor containing paste and bake them on the ceramic substrate 111.

COMPARATIVE EXAMPLE 6 Manufacture of Ceramic Heater (Resistance HeatingElement Formation by Laser Trimming)

[0370] A ceramic heater was manufactured in the same manner as Example15 except that the resistance heating element was formed by using aconductor containing paste having the following composition and heatingand firing the paste.

[0371] The conductor containing paste was a silver paste with acomposition same as that in Example 15. The silver particle (Ag-128,made by Shouei Chemical Products Co., Ltd.) had an average particlediameter of 0.6 μm and a spherical shape.

[0372] The viscosity of the conductor containing paste was 80 Pa·s.

[0373] Further, after the conductor containing paste layer in theresistance heating element patterns was formed, the ceramic substrate111 was heated and fired at 780° C. for 20 minutes to sinter silver andlead in the conductor containing paste and bake them on the ceramicsubstrate 111.

[0374] Evaluation Method

[0375] (1) Measurement of Surface Roughness Ra of Conductor Layer(Resistance Heating Element)

[0376] The surface roughness Ra of the surface of the resistance heatingelement (the conductor layer) on the ceramic substrate formed in each ofthe above-mentioned Examples and Comparative Examples was measuredaccording to JIS B 0601 using a surface roughness measurement apparatus(Therfcom 920A manufactured by Tokyo Seimitsu Co., Ltd.). The surfaceroughness Ra obtained from the measurement results was shown in Table 1.The charts showing the measurement results of Example 14 and Example 15were respectively shown in FIG. 17 and FIG. 18.

[0377] (2) Measurement of Gutter Shape

[0378] In Examples 14, 16, 17 and Comparative Example 5, after theresistance heating element was formed on the ceramic substrate andgutters were formed on the resistance heating element, the width and thedepth of the gutters were measured. Further, in Example 15 andComparative Example 6, after the conductor layer was formed on theceramic substrate, gutters were formed in the portions of the conductorlayer to be removed and the width and the depth of the gutters weremeasured. The width and the depth of the gutters were measured by alaser displacement meter manufactured by Kience Co. The results wereshown in Table 4.

[0379] (3) Temperature Measurement of Heating Face

[0380] After the ceramic heater according to each of the above-mentionedExamples and Comparative Examples was heated to 300° C., the temperatureof the heating face of the ceramic substrate was measured by athermoviewer (IR-162012-0012, manufactured by Nippon Datam Co.) and thetemperature difference between the lowest temperature and the highesttemperature was calculated. The results were shown in Table 4. Thetemperature difference in Table 4 means the temperature differencebetween the lowest temperature and the highest temperature.

[0381] (4) Occurrence of Crack Formation

[0382] Regarding each ceramic heater of Examples 14 to 19 andComparative Examples 5, 6, a glass layer with a thickness of 10 μm wasformed by applying a glass paste (borosilicate glass) comprising 50parts by weight of a glass powder with an average particle diameter of0.5 μm, 20 parts by weight of ethyl alcohol, and 5 parts by weight ofpolyethylene glycol to the surface and firing the paste at 1500° C.

[0383] The resulting ceramic heater was heated to 200° C. in an oven andimmersed in water at 25° C. in order to observe the occurrence of thecracks in the glass layer.

[0384] For the ceramic heaters of Examples 14 to 18, no crack wasobserved. However, for the ceramic heaters of Example 19 and ComparativeExamples 5 and 6, cracks were found formed. TABLE 4 Surface roughness Raof conductor Temperature layer (resistance Shape of gutters (μm)difference of heating element) Width Depth heating face (μm)(dispersion) (dispersion) (° C.) Example 0.8 50 (0.5) 5 (0.05) 0.5 14Example 0.3 50 (0.5) 5 (0.05) 0.5 15 Example 9.8 50 (0.1) 5 (0.01) 0.516 Example 15 50 (0.1) 5 (0.02) 0.6 17 Example 0.01 50 (0.5) 5 (0.05)0.6 18 Example 18 50 (1.0) 5 (0.1) 1.5 19 Compara- 0.007 50 (5.0) 5(2.0) 5.0 tive Example 5 Compara- 0.005 50 (4.8) 5 (1.9) 4.8 tiveExample 6

[0385] As being made clear from the results shown in Table 4, in ceramicheaters according to Examples 14 to 19, gutters were formed in theresistance heating elements by irradiating laser beam to the resistanceheating elements having a surface roughness Ra of 0.01 μm or more andperforming trimming, and the formed gutters had a width of 50 μm and adepth of 5.0 μm as designed. Accordingly, the resistance values of theresistance heating elements could precisely be adjusted and thetemperature difference between the highest temperature and the lowesttemperature in the heating faces of the ceramic substrate was small.

[0386] In Example 15, the resistance heating element was formed byperforming trimming and since the trimming was carried out byirradiating laser beam to the conductor layer with a surface roughnessRa of 0.01 μm or more, precise patterns were formed and the temperaturedifference between the highest temperature and the lowest temperature inthe heating face was small.

[0387] On the other hand, in the case of the ceramic heater according toComparative Example 5, the surface roughness Ra of the resistanceheating element was less than 0.01 μm and the surface was so flat thatthe laser beam was reflected, and gutters could not be formed byperforming trimming, and the resistance value of the resistance heatingelement could not be controlled, and the temperature difference betweenthe highest temperature and the lowest temperature in the heating faceof the ceramic substrate was too large for practical use.

[0388] Also, in the case of the ceramic heater according to ComparativeExample 6, since the surface roughness Ra of the resistance heatingelement was less than 0.01 μm, the surface was so flat that the laserbeam was reflected, and gutters could not be formed by performingtrimming, and the resistance heating element with designed patternscould not be formed, and portions of conductor layer which should beremoved were left and consequently, the temperature difference betweenthe highest temperature and the lowest temperature in the heating faceof the ceramic substrate became too large.

[0389] Among the ceramic heaters according to Examples, the ceramicheater according to Example 19 had the largest temperature differencebetween the highest temperature and the lowest temperature in theheating face. It was supposed to be attributed to the fact that thesurface roughness was so high to make the dispersion of the resistancevalue of the resistance heating element wide, resulting in the largetemperature difference.

[0390] As described above, in the ceramic heaters obtained in Examples,laser beam was irradiated to the resistance heating element or theconductor layer with a surface roughness Ra of 0.01 μm or more toperform trimming, so that incomplete trimming of the resistance heatingelement or the conductor layer owing to reflection of the laser beamnever took place and precise patterns were easily formed and grooveswith a precise width was able to be formed.

INDUSTRIAL APPLICABILITY

[0391] As described above, the ceramic heater according to the firstaspect of the present invention comprises a resistance heating elementwith a small resistance change ratio, has a sufficient temperaturerising and temperature dropping speed and is excellent in temperaturecontrollability. Also, corrosion resistance to the reactive gases in asemiconductor producing device is also excellent and the insulatingcovering is of an insulator, so that the resistance value of theresistance heating element can be made high and the heater can be usedas a heater for a middle temperature or a high temperature use.

[0392] Further, in the case the insulating covering is formed in thestretch of given area including the resistance heating element-formedarea, the above-mentioned effects are provided and also migration ofmetal such as silver can be prevented. Further, since the covering iseasy, the formation cost of the insulating covering can be reduced.

[0393] According to the ceramic heater manufacturing method of thesecond aspect of the present invention, since the resistance value ofthe resistance heating element is adjusted by irradiating laser beam tothe resistance heating element having a surface roughness Ra of 0.01 μmor more according to JIS B 0601 and performing trimming, reflection oflaser beam can be prevented and the resistance heating element can betrimmed as designed and consequently, the resistance value of theresistance heating element can precisely be adjusted.

[0394] Also, according to the ceramic heater manufacturing method of thethird aspect of the present invention, since the resistance heatingelement in given patterns is formed by irradiating laser beam to theconductor layer having a surface roughness Ra of 0.01 μm or more basedon JIS B 0601 and performing trimming, reflection of laser beam can beprevented and the unnecessary portions of the conductor layer can betrimmed as designed and consequently, a ceramic heater having precisepatterns and excellent in the temperature evenness of the heating facecan be obtained.

[0395] Further, according to the ceramic heater of the fourth aspect ofthe present invention, since the surface roughness of the resistanceheating element surface is high, the atmosphere gas can be stagnated andair can be prevented from flowing in the gutters and the cuts in theresistance heating element to suppress formation of low temperatureportions owing to the existence of the cuts and gutters. Consequently,the temperature evenness of the heating face can be improved further.

1. A ceramic heater comprising: a ceramic substrate; a resistanceheating element, which is composed of one circuit or more circuits,disposed on a surface of a ceramic substrate; and an insulating coveringprovided on said resistance heating element, wherein said insulatingcovering has a surface roughness Ra of 0.01 to 10 μm in accordance withJIS B
 0601. 2. The ceramic heater according to claim 1, wherein saidinsulating covering is formed in a stretch of area containing a portionon which said circuits are formed.
 3. The ceramic heater according toclaim 1 or 2, wherein said ceramic substrate comprises a nitride ceramicor a carbide ceramic.
 4. The ceramic heater according to any of claims 1to 3, wherein said insulating covering comprises an oxide glass.
 5. Theceramic heater according to any of claims 1 to 3, wherein saidinsulating covering comprises a heat resistant resin material.
 6. Theceramic heater according to claim 5, wherein said heat resistant resinmaterial is one kind or more selected from a polyimide type resin and asilicone type resin.
 7. The ceramic heater according to any of claims 1to 6, wherein a heating face is a side opposed to the side on which saidresistance heating element is formed.
 8. The ceramic heater according toany of claims 1 to 7, wherein said insulating covering covers theresistance heating element comprising two or more circuits in a lump. 9.A method for manufacturing a ceramic heater comprising the steps of:forming a resistance heating element having a given pattern on a surfaceof a ceramic substrate; and irradiating laser beam onto said resistanceheating element to form a gutter or a cut after the preceding step so asto adjust a resistance value of the resistance heating element, whereinwhen said resistance heating element is formed on the surface of saidceramic substrate, a surface roughness Ra of said resistance heatingelement is 0.01 μm or more in accordance with JIS B
 0601. 10. A methodfor manufacturing a ceramic heater comprising the steps of: forming astrip-shaped or a ring-shaped conductor layer on a given area of asurface of a ceramic substrate; and irradiating laser beam onto saidconductor layer to remove a part of said conductor layer by performingtrimming after the preceding step so as to form a resistance heatingelement having a given pattern, wherein when the conductor layer isformed on the surface of said ceramic substrate, a surface roughness Raof said conductor layer is 0.01 μm or more in accordance with JIS B0601.
 11. A ceramic heater comprising: a ceramic substrate; and aresistance heating element formed on a surface of said ceramicsubstrate, wherein a gutter or a cut is formed at a part of saidresistance heating element, and said resistance heating element has asurface roughness Ra of 0.01 μm or more in accordance with JIS B 0601.12. The ceramic heater according to claim 11, wherein said resistanceheating element is covered with an insulating layer.